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BIOLOGY
Biology: the study of life
Organisms: all living things
There have been different views of life throughout history.
1. vitalism: living things exist because they have been
filled with special forces, called ethers, which bring
nonliving things to life
Vitalism was the main view of life for about 2000
years until the Dark Ages, when the idea of
spontaneous generation came around.
2. spontaneous generation: a theory stating that living
organisms are produced from nonliving matter and
ethers
examples: maggots from rotting meat
mice from old rags
geese from river banks
1668 – Francesco Redi tests spontaneous generation. Redi
thought that maggots came from flies, not from ethers. So he
put some rotting meat in jars.
1. When the jars were left open  maggots
appeared
(Both flies and ethers could get into the jar. What
does this show?)
2. When the jars were sealed  no maggots
(Neither the ethers nor the flies could get into the
jar. What does this show?)
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3. When the jars were covered with cloth  no
maggots
(Ethers could get in but flies could not. What
does this show?)
Redi’s experiment supported another theory that eventually
replaced spontaneous generation  biogenesis.
3. biogenesis: principle that life comes only from life
“bio” = life
“gen” = to make, produce
 Each type of living organism produces more of its
own kind.
But it wasn’t as if everyone let go of spontaneous generation
and immediately embraced biogenesis. In fact, Redi’s work
and conclusions were questioned and tested for the next 200
years.
Background info: Microorganisms (bacteria, protists, etc.)
were first observed around the same time as Redi was
completing his maggot experiments.
John Needham – mid 1700’s – English scientist
 claimed that spontaneous generation could occur
under the right conditions
 Needham sealed a bottle of gravy and heated it. He
claimed that the heat would kill any living things in the
gravy. After several days, the gravy was teeming with
microorganisms.
 Needham’s (incorrect) conclusion: The microorganisms only could have come from the gravy itself.
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Rebuttal of Needham’s Work:
Lazzaro Spallanzani – Italian scientist
 He thought that Needham had not heated his
samples of gravy to a temperature high enough.
 Spallanzani boiled 2 flasks of gravy. He assumed
that boiling would be enough to kill any microorganisms already in the gravy.
 Immediately after boiling, he sealed one of the flasks
of gravy. The other was left open.
 After a few days, the open jar was full of microorganisms. The sealed jar had none.
 Spallanzani’s Conclusion: Gravy did not produce
microorganisms. The microorganisms in the open
jar had come from microorganisms in the air that
had multiplied in the gravy.
Despite Spallanzani’s work, some scientists still continued to
support spontaneous generation well into the 1800’s. They
argued that air contained a “life force” necessary for
generating life, and therefore Spallanzani’s work was not
conclusive.
Louis Pasteur – 1864 – French scientist
 Designed a flask to settle the argument.
 The flask had a long curved neck. Air could get in,
but microorganisms from the air could not make
their way through the neck into the flask.
 Broth was boiled in this flask and without being
sealed, it remained free of microorganisms for an
entire year. As long as it was protected from
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microorganisms, the broth remained free of living
organisms.
 After one year, Pasteur broke off the curved neck of
the flask, and the broth quickly filled with microorganisms.
Pasteur’s experiment finally convinced other scientists that
spontaneous generation was incorrect. It also provided very
strong support for biogenesis.
Louis Pasteur’s Test of Spontaneous Generation
Broth is boiled.
Broth is free of
microorganisms
for one full year.
Curved neck is
is removed.
Broth is
teeming with
microorganisms.
Side Note: We’ve been talking about hypotheses and
theories. The word “theory” has a different meaning in
science than in other areas. In science, a theory is a well
tested explanation that unifies a broad range of observations.
Theories are extremely well supported by vast amounts of
experimentation, data collection, and scrutiny. It is not an
“educated guess” like a hypothesis.
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As more information is gained with advances in technology
and further research, a theory is constantly analyzed,
reviewed, and if necessary, revised.
Properties of Life
I. Living things are made up of units called cells.
II. Living things reproduce.
III. Living things are based on a universal genetic code.
IV. Living things grow and develop.
V. Living things obtain and use materials and energy.
VI. Living things respond to their environment.
VII. Living things maintain a stable internal environment.
VIII. Taken as a group, living things change over time.
We’re going to take a brief look at each one of these
properties and later in the course, take a much deeper look
at some of them. Remember, every textbook you pick up
could have a different list. There is no set list of properties
that is universally accepted.
I.
Living things are made up of cells.
Cell – collection of living matter enclosed by a barrier
that separates the cell from its surroundings; basic
unit of all forms of life
A. Cells can grow, respond to the environment, and
reproduce; they are complex and highly organized.
B. Organisms can be made of one cell or many cells.
1. unicellular – “single celled” – organisms
consisting of only one cell
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2. multicellular – “many celled” – organisms
consisting of hundreds, even trillions of cells
a. often has a diversity of cells with different
functions
b. sizes and shapes of cells differ also within
the organism
II. Reproduction
A. All organisms produce new organisms through
reproduction.
B. Two basic kinds of reproduction:
1. sexual reproduction:
a. cells from 2 different parents unite to
produce the first cell of the new organism
b. the majority of multicellular organisms use
sexual reproduction
2. asexual reproduction:
a. a single parent reproduces by itself
b. there are many different ways that asexual
reproduction can happen
 a single celled organism divides in half
to form 2 new organisms
 a portion of an organism splits off to
form a new organism
III. Based on a Genetic Code
A. Traits are inherited from parent to offspring. In
asexual reproduction, parents and offspring have
the same traits. In sexual reproduction, offspring
are different from their parents, within limits.
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B. DNA, or deoxyribonucleic acid, is the molecule that
holds the directions for these patterns of
inheritance.
C. Every single living organism has DNA, the genetic
code.
IV. Growth and Development
A. All living things grow during at least part of their
lives.
growth – increase in size
B. Multicellular organisms also go through a process
called development.
1. As cells divide in early stages of life, they
change in shape and structure to form cells
such as liver cells, brain cells, lung cells, etc.
2. This process is called differentiation (also
called cell specialization) – process in which
cells become specialized in structure and
function
V. Need for Materials and Energy
A. To grow, develop, reproduce, and just to stay alive,
living things need energy and materials.
1. metabolism: set of chemical reactions through
which an organism builds up or breaks down
materials as it carries out life processes
2. Organisms have many different ways of
obtaining energy from their environments.
a. plants, some bacteria, most algae –
photosynthesis
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b. other organisms eat those organisms that
use photosynthesis
c. There are other chemical ways besides
photosynthesis to get energy from the
environment, but they are not very
common. e.g. chemoautotrophs
VI. Response to the Environment
A. Organisms detect and respond to stimuli in the
environment.
1. stimulus (plural stimuli) – a signal to which an
organism responds
2. internal stimulus – comes from within the
organism
e.g. hungry feeling when sugar levels are low
3. external stimulus – environment outside the
organism gives a signal
e.g. sunlight amounts, temperatures, gravity
VII. Maintaining an Internal Balance
A. Though conditions in the environment can vary
widely, internal conditions for organisms must be
kept fairly constant e.g. temperature, hydration.
1. homeostasis – process by which organisms
maintain a relatively stable internal
environment
2. often involves internal feedback systems
e.g. too hot – body sweats to cool itself
too cold – body shivers to produce heat
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VIII. Evolution
A. Although individual organisms go through changes,
the basic traits they inherited from their parents do
not - eye color, skin color, etc.
1. However, as a GROUP, any given kind of
organism can evolve, or change over time.
2. It takes a very long time for change to appear,
hundreds, thousands, even millions of years.
B. The ability for a group of organisms to change over
time is invaluable for survival in a world that is
always changing.
How might global warming affect evolution?
Branches of Biology and the Organization of Life
Life has many different levels of organization. All of them
are open to study and have different specialties associated
with them. The following section is a hierarchy, or
arrangement, of these levels of life.
1. atoms & molecules: Atoms are the smallest parts of
ALL MATTER, living or nonliving. Molecules are
groups of atoms and have different properties than the
atoms by themselves.
2. cell: made up of groups of atoms and molecules;
smallest unit of life
3. tissue: group of similar cells that perform a specific
function; examples – muscle, bone, blood
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4. organ: group of tissues that work together to perform
closely related functions ex. – heart, leaves, kidneys
5. organ system: group of organs working together to
perform a specific function; ex. digestive, circulatory
6. organism: an individual living thing
7. population: group of organisms of one type that live in
a particular area
ex. snapping turtles in Farmer Smith’s pond
Yellow bellied sapsuckers living in Raccoon
Creek State Park
8. communities: all of the populations that live together
in a defined area
ex. the lawn in your front yard – worms, ants,
beetles, grass, fungi (BUT NOT the water, soil,
minerals, sunlight, and rain)
9. ecosystem: the community and its nonliving
surroundings
10. biosphere – the parts of the Earth that contain all
ecosystems
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Chemistry of Life
Inorganic and organic compounds – life needs some of each.
Organic: includes most compounds that contain carbon;
usually associated with living things
example: calcium carbonate CaCO3
Inorganic: compounds that generally don’t contain
carbon
example: salt (sodium chloride) NaCl
Organisms are composed of 4 major classes of
macromolecules (big molecules) plus water.
1. Proteins: made of amino acids
 functions: give structure to the body;
speed up chemical reactions
Note: Proteins that speed up chemical reactions are
called enzymes. Not all proteins are enzymes.
2. Lipids: fats, waxes, steroids
 functions: store energy; make up a part of
membranes; act as hormones
3. Carbohydrates: sugars, starches
 function: source of energy
4. Nucleic Acids: DNA and RNA
 functions: contain genetic information
help to make proteins
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Other chemistry affecting life: pH
Solutions may be acidic, basic, or neutral. It depends on how
many hydrogen ions (H+) there are compared to how many
hydroxide ions (OH ) there are.
Ion: an atom with an electrical charge due to a loss
or gain of electrons
pH scale: standard measurement of concentration of
H+ ions in solution
The pH scale ranges from 0 to 14.
0 up to 7 is acidic
7.0 = neutral
above 7 to 14.0 is basic
pH is important because it affects the rates of chemical
reactions, often making them happen very fast or very slow
depending on the reaction and how the pH changes.
*Be sure to study the diagram pages about ions and atoms!
I. Microscopes
A. Two main types
1. light microscope: produces magnified images by
focusing visible light rays
2. electron microscope: produce magnified images
by focusing beams of electrons
B. Two main problems in making microscopes
1. What is the instrument’s magnification?
a. how much larger can it make an object
appear than its real size?
2. How sharp an image can the microscope
produce?
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C. Light Microscopes
1. most commonly used
2. magnification is about 1000x
3. compound light microscope: allows light to pass
through the specimen (what you’re looking at)
and uses 2 lenses to form an image
a. can view dead organism and their parts
b. can view some tiny organisms and cells while
living
4. Methods to improve using a light microscope
a. chemical stains to show specific structures in
cells and other specimens
b. using video cameras and computer processing
to produce moving 3D images
5. Main advantages:
a. very affordable
b. easy to use
6. Main disadvantages:
a. magnification is very limited
b. images can often be grainy, poor quality
D. Electron Microscopes
1. primarily used to see extremely tiny objects
2. magnification is vastly greater than light
microscopes
3. two main types of electron microscopes
a. transmission electron microscopes (TEMs) shine a beam of electrons through a thin
specimen
 can reveal lots of detail inside the cell
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 samples must be preserved and dehydrated
(nothing living)
b. scanning electron microscope (SEMs) –
scans a narrow beam of electrons back and
forth across the surface of a specimen
 produce realistic and detailed 3D images of the
surfaces of objects
 the images are often quite surprising in their
details
 like TEMs, samples must be preserved and
dehydrated
4. Main Advantages
a. pictures are spectacular
b. the magnification is fantastic
5. Main Disadvantages
a. extremely expensive
b. need extensive training to use
E. In the 1990’s, scientists perfected a new type of
microscope, the scanning probe microscope.
1. produces images by tracing the surfaces of
samples with a fine probe
2. now possible to view single atoms
3. can operate in ordinary air (SEMs and TEMs
need a vacuum) and can show samples in solution
4. revolutionizing what and how we study many
small particles
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Cell Theory
Before the invention of the microscope, people knew only
about organisms that they could see with the unaided eye.
Late 1500’s: microscope invented
1590: Zacharias Janssen invents the 1st compound
microscope
 early microscopes were used as toys
1665: English physicist Robert Hooke used a microscope to
look at cork. He called the empty spaces in rows
“cells” because they reminded him of the tiny rooms
in a monastery (which are also called cells). Scientists
began using microscopes for investigating everything.
1674:
Anton van Leeuwenhoek (Dutch) – 1st person to see
living organisms under the microscope; examined
things like blood and pond water
 Leeuwenhoek called the tiny creatures he saw
“animalcules” which means “little animals”
1838: German botanist Matthias Schleiden concluded that
all plants are made of cells
1839: German zoologist Theodore Schwann concluded that
all animals are made of cells; he later concluded that
all living things are made of cells
1855: German doctor Rudolf Virchow reasoned that new
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cells only come from already existing cells
The ideas of Schleiden, Schwann, and Virchow make up what
is known as the cell theory. It has 3 main points:
1. Cells are the basic units of life.
2. All organisms are made of one or more cells.
3. New cells are produced from existing cells.
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Parts of the Cell
Cell structure is one way in which organisms differ from each
other. For example, animal cells have things in them that
plant cells do not, and muscle cells have structures in them
that aren’t found in blood cells. But there are certain
features that are common to most cells.
I.
Cell Membrane:
A. cell membrane: a thin layer of lipids and proteins
that separates the cell’s contents from the outside
environment
 very thin: 10,000 stacked = thickness of a page
1. function: controls what enters and leaves the cell
2. composition: mostly phospholipids and some
proteins
B. Phospholipids look like this:
phosphate head is hydrophilic (“water loving”)
lipid tails are hydrophobic (“water fearing”)
C. Cell membranes consist of 2 phospholipid layers, called a
bilayer. The phosphate heads face the watery fluids
inside and outside of the cell. The lipid tails are
sandwiched inside the bilayer.
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D. Embedded in this bilayer are 3 different kinds of
proteins.
1. channel protein: allows some molecules to pass
through the membrane
 shaped like a doughnut; only certain molecules are
able to go through
2. receptor proteins: transfer information from the
world outside the cell to the inside of the cell
 look like boulders
How do they work? The end of the receptor protein
that sticks out from the cell surface has a special
shape that will hold only one particular type of
molecule. When a molecule of the right shape comes
along, it causes changes at the other end of the
protein, which causes other responses inside the cell.
3. marker proteins: act as name tags for cells which can
be used for identification and organization
 long, thin proteins often with carbohydrates on
their surfaces
The cell membrane is very complex. It is fluid (flows like a
liquid). And you know it’s made of different pieces that can
move around in the membrane. These properties have given
this view of the cell membrane’s structure a certain name:
the fluid mosaic model
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II. The Nucleus
A. function: control center of the cell; surrounded
by a membrane called the nuclear membrane
 Most (but not all) cells have a nucleus, some
cells even have more than one.
NB: ALL cells contain DNA, but the DNA isn’t always
located in a nucleus.
B. The nucleus contains DNA (deoxyribonucleic acid),
which carries all of the instructions for cell activity.
a. Usually the DNA is in a long strand called
chromatin.
b. However, during cell division, the chromatin
coils into thick chromosomes.
C. A nucleus (plural = nuclei) usually contains a
nucleolus (plural = nucleoli). The nucleolus makes
ribosomes (which are small parts of the cell that
make proteins).
D. The nucleus is used to classify cells into 2 types:
1. prokaryotic cells: cells that never contain a
nucleus
 still have DNA but it’s not in a special
compartment like the nucleus
 organisms whose cells are prokaryotic are
called prokaryotes
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2. eukaryotic cells: always or usually contain a
nucleus
 organisms whose cells are eukaryotic are
called eukaryotes
BACTERIA & THEIR RELATIVES ARE PROKARYOTES.
ALL OTHER ORGANISMS ARE EUKARYOTES.
III. Cytoplasm
A. cytoplasm: everything inside the cell membrane
except the nucleus ( in eukaryotic cells) or the DNA
(in prokaryotic cells)
1. made of 2 things: cytosol and organelles
cytosol: jellylike mixture that consists mostly of water,
along with proteins, carbohydrates, and other organic
compounds
organelles: structures that work like miniature organs,
carrying out the specific functions in the cell
 In eukaryotic cells, most organelles are surrounded
by membranes. In prokaryotic cells, there are no
membrane bound organelles (with one exception ribosomes).
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IV. Cytoskeleton
A. Definition: a network of protein filaments within
some cells that helps the cell maintain its shape
and is involved in many forms of cell movement
B. Two main parts of cytoskeleton – microfilaments
and microtubules
1.
Microfilaments: threadlike structures
made of a protein called actin
a. Microfilaments form extensive networks
and produce a tough, flexible
framework that supports the cell.
b. They also help cells to move – assembly
and disassembly of microfilaments is
responsible for cells being able to crawl
along surfaces
2.
Microtubules: hollow structures made up
of proteins called tubulins
a. Microtubules help the cell maintain its
shape.
b. They are very important in cell division
(form the mitotic spindle).
c. They also help to build projections on
the cell surface like cilia and flagella,
which are used to move the cell.
d. In ANIMAL CELLS ONLY,
microtubules form centrioles. Located
near the nucleus, the centriole helps to
organize cell division.
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Organelles of Eukaryotic Cells
1. mitochondria: the “powerhouse” of the cell
function: . release the energy in food by breaking down
food molecules
2. endoplasmic reticulum (ER): the “highway” of the cell;
it’s a system of membranes used to transport materials
around the cell and to process certain macromolecules
There are 2 types of ER:
a. rough ER: has ribosomes attached to it
b. smooth ER: does not have ribosomes
attached
3. ribosomes: structures where proteins are made; can be
attached to the ER or free floating in cytoplasm
4. Golgi Apparatus: the “post office” of the cell; it’s a series
of membranes stacked like pancakes
function: adds the finishing touches on newly made
molecules and then packages those molecules
and sends them out into the cell
5. lysosomes: small sacs that contain enzymes used to digest
food particles
6. chloroplasts: make food from sunlight, water, and carbon
dioxide through photosynthesis
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 CHLOROPLASTS ARE ONLY FOUND IN THE
CELLS OF GREEN PLANTS AND ALGAE!!!
7. vacuoles: membrane bound spaces that hold or store
wastes, water, and nutrients
 very large in plant cells, small or not found in animal cells
The 7 organelles just described are found only in eukaryotic
cells, with the exception of ribosomes. Ribosomes are found
in both eukaryotic and prokaryotic cells. All other organelles
are found ONLY in eukaryotic cells.
Kinds of Eukaryotic Cells: Animal Cells vs. Plant Cells
Plant cells have a few extra organelles and structures:
chloroplasts, large vacuoles, and the cell wall
cell wall: extra layer that lies outside the cell membrane;
made mostly of cellulose (a type of sugar)
function: gives strength and rigidity to the cell
In addition to plants, the cells of algae, fungi, and some
bacteria have cell walls.
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Comparing Prokaryotic and Eukaryotic Cells
Prokaryotic
Structure
Cell Membrane
Cell Wall
Nucleus
DNA
Ribosomes
Endoplasmic
Reticulum
Golgi Apparatus
Lysosomes
Vacuoles
Mitochondria
Chloroplasts
Bacteria &
Relatives
Eukaryotic
Plant Cell
Animal
Cell
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ENDOSYMBIOTIC THEORY
How did eukaryotic cells develop?
This was a question that was on the minds of many scientists.
Over 100 years ago, the idea of endosymbiotic theory was
proposed. But it wasn’t until Lynn Margulis of Boston
University championed the theory in the 1960’s that it became
mainstream thinking.
Endosymbiotic theory: theory that eukaryotic cells formed from
a symbiosis among several different prokaryotic organisms
Symbiosis: any relationship in which two species live together
closely
As scientists studied eukaryotic cells, they noticed a few things:
1. some organelles had membranes just like
prokaryotes (mitochondria, chloroplasts)
2. some organelles had their own DNA that was very
similar to prokaryotic DNA
3. some organelles had their own ribosomes whose size
and structure closely resemble those of prokaryotes
4. some organelles divided separately from the rest of
the cell (used same way to divide as prokaryotes)
They came up with the idea that a much larger cell had
engulfed (surrounded) a bacterium and instead of being
digested as food, that bacterium remained inside the cell.
Eventually, these engulfed bacteria lost their ability to live on
their own and became organelles within the larger cell. The
result was a eukaryotic cell.
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Size of Cells
If you compare cells from an elephant with cells from a
mouse, they are very much alike in shape, structure, and size.
Almost all eukaryotic cells are about 10 m to 100 m big.
(m = micrometer)
Size often depends on the cell membrane. Cells obtain
nutrients and get rid of wastes through the cell membrane.
 The bigger the cell, the more membrane that is needed.
Problem: As cells get bigger, there is less surface area of the
cell (where the membrane is) for each part of volume (where
the cytoplasm with the organelles is located).
As cells increase in size, their volume increases more rapidly
than the surface area does. With a really big volume, it’s
very hard for the cell to transport things in and out of the cell
fast enough.
Another factor is the nucleus. The nucleus can only control
so much cytoplasm and keep up with the cell’s activities.
So the cell has to stay small to survive.
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Diffusion and Osmosis
Cells need a way to move water molecule, food particles, and
other materials through their membranes. Some things, like
water, pass through freely. Others have to be carried
through channels.
Terms to know and understand
Solute: substance that is dissolved in a solvent to make a
solution
Solvent: substance in which a solute is dissolved to form a
solution
e.g. saltwater – salt is the solute, water is the solvent
I.
Diffusion: mixing of 2 substances by the random motion
of molecules
A. molecules move from an area of high concentration to
an area of low concentration
B. When the molecules are spread out evenly, diffusion
stops because there is no longer a concentration
gradient
concentration gradient: the difference between the
concentration of a particular molecule in one area and
the concentration of the same molecule in an adjacent
area (adjacent = beside)
 When the concentration of the solute is the same
throughout a system, the system has reached equilibrium.
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II. Osmosis: diffusion of water across a semipermeable
membrane (semipermeable = only certain things get
through)
 Water moves across a membrane from a region of high
concentration of water to an area of low concentration
of water
III. Facilitated Diffusion
A. facilitated diffusion: another type of movement of
particles where particles diffuse across cell
membranes with the help of proteins in the
membranes
1. particles always move DOWN the concentration
gradient going from high concentration to low
concentration
 facilitated diffusion increases the rate that
some particles cross the cell membrane
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Passive Transport vs. Active Transport
 The processes of diffusion, osmosis, and facilitated
diffusion DO NOT require any energy to be used by
the cell.
 For this reason, these 3 processes can be called passive
transport.
 When a cell uses energy to move particles across the
membrane, those processes can be described as active
transport.
IV. Active Transport
A. Sometimes the cell has to move things against (or up)
the concentration gradient, going from low
concentration to high concentration. This requires
energy, so it’s called active transport.
1. Like facilitated diffusion, active transport
uses proteins to move particles, but now it
takes energy.
2. example: sodium – potassium ion pump
 uses active transport to keep the right
balance of sodium and potassium ions in
and out of the cell
 This balance is crucial for muscle
contraction, nutrient absorption, and
nerve pulse transmission.
V. Bulk Transport
A. Bulk transport is used to move large particles in and
out of the cell. During bulk transport, large particles
move across the cell membrane by being packaged in
membrane-bound sacs.
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B. There are 2 types of bulk transport: exocytosis and
endocytosis
1. Exocytosis: material is moved from inside the cell
to outside the cell ( “exo” = exit )
a. wastes and cell products are packaged by the
Golgi body in sacs called Golgi vesicles
b. the vesicles then fuse with the cell membrane
and the materials are secreted outside of the
cell
(outside the cell)
#1
#2
#3
Vesicle
2. Endocytosis: material is brought into the cell
a. a portion of the cell membrane surrounds a
particle that is outside of the cell
b. the cell pinches off a saclike portion of its outer
membrane to form a new vesicle
 once inside the cell, the vesicle can fuse
with other organelles or release its
contents into the cytoplasm
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(outside the cell)
#1
#2
inside the cell (cytoplasm)
#3
3. Two types of endocytosis:
a. pinocytosis: cell membrane encloses a
droplet of fluid to bring into the cell
b. phagocytosis: cell engulfs a solid substance to
bring into the cell
 human white blood cells use phagocytosis
to engulf and destroy bacteria and other
invaders of the body
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Hypertonic, Hypotonic , and Isotonic Solutions
1. Hypertonic solution: the concentration of solutes (in the
solution) is HIGHER than the concentration of solutes
inside the cell
 water diffuses OUT of the cell
example: potatoes in salt water – water left the cells and
the potatoes became very flexible (no water to make the
cells rigid)
2. Hypotonic Solution: concentration of solutes (in the
solution) is LOWER than the concentration of solutes
inside the cell
 water diffuses INTO the cell
example: potatoes in distilled water – water came into
the cells, causing the cells to swell and making the potato
rigid
3. Isotonic Solution: concentration of solutes (in the
solution) EQUALS the concentration of solutes inside the
cell
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ENERGY
Life depends on energy, which is stored in the chemical
bonds of energy storing compounds. One of the most
important energy compounds is ATP (adenosine
triphosphate).
I.
ATP
A. made of a sugar, adenine, and 3 phosphates
1. ATP releases chemical energy whenever a bond
holding a phosphate is broken
A
A
S
P
P
P
Energy released when
bond is broken
Adenine
2. The result is ADP – adenosine diphosphate
A
Adenine
A
S
P
P
B. ATP is used for doing work in the cell
1. provides energy for the mechanical functions of
cells
2. provides energy for active transport of molecules
and ions across the cell membrane
3. used in making and breaking down large
molecules
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C. Because cells are constantly at work, they need an
endless supply of ATP
1. ATP comes from attaching a phosphate to an ADP
2. The cycle of making and breaking down ATP
molecules occurs constantly in cells
 10 million new ATP molecules are made
EVERY SECOND in the cell
II. Sources of Energy
Organisms are classified into 2 groups according to how
they get food: autotrophs and heterotrophs
A. Autotrophs: can make their own food
Ex. green plants use CO2 , water, and sunlight to
make food
1. the foods made by autotrophs are mainly
carbohydrates such as glucose
2. autotrophs are called producers because they
produce their own food
3. producers are vital to the world: they are a
source of food for all other organisms, directly or
indirectly
B. Heterotrophs: organisms that can’t make their own
food
1. must eat, or consume, other organisms for food
2. heterotrophs are called consumers
35
I.
Photosynthesis
Photosynthesis is the process by which autotrophs
convert sunlight into a usable form of energy
A. autotrophs that perform photosynthesis contain
pigments
1. pigment: molecule that absorbs certain
wavelengths of light and reflects others
 whatever wavelength is reflected is the
color you see
2. chlorophyll: pigment that is used in photosynthesis
 absorbs blue, violet, and red light
 reflects green light, gives the green color of
many plants
B. In many autotrophs, the pigments (including
chlorophyll) are in specialized organelles
 chlorophyll is located in the chloroplasts
II. Photosynthesis in a Nutshell
A. 6 CO2 + 6 H2O
carbon
dioxide
water
Light
energy
C6H12O6 + 6 O2
glucose
oxygen
1. The energy stored in glucose is used later to
produce ATP.
36
B. Photosynthesis does NOT happen all at once. There
are 2 distinct stages.
1. The first stage is called the light dependent
reactions.
a. begins with light hitting the chloroplast
b. water is split into hydrogen ions, oxygen,
and excited electrons
 oxygen diffuses out of the chloroplast
 NADPH and ATP are produced
(NADPH is another energy storing molecule)
LIGHT REACTIONS OCCUR IN THE THYLAKOID.
2. The second stage of photosynthesis is called the
Calvin Cycle. (also called the “dark reactions”)
a. the ATP and NADPH from the light dependent
reactions are used in the Calvin cycle
b. the Calvin cycle uses CO2 to produce sugar
(glucose is a type of sugar)
III. Details: The Light Reactions
A. occur in different areas of the thylakoid called
Photosystem I and Photosystem II, which are light
collecting units of the chloroplast
1. Sunlight comes into Photosystem II and splits
water into H+ ions (hydrogen ions), oxygen (O2),
and energized electrons (e-- ).
37
—
2. The excited e go through the electron transport
chain to Photosystem I.
 carrier molecules (of the e— transport chain)
use the electrons’ energy to actively
transport H+ ions from the stroma to the
thylakoid
IV. Calvin Cycle – Details (a.k.a. Dark Reactions)
A. The Calvin Cycle :
1. Requires the products of the light dependent
reactions
2. Requires the input of CO2
3. Takes place in the stroma of the chloroplast
B. Process:
1. CO2 is used to build molecules of glucose
2. ATP and NADPH are used for energy and
hydrogen (from light dependent reactions)
3. 1 molecule of glucose is made for every 6
molecules of CO2 in the cycle
V. Now what?
A. Photosynthesis gets glucose from the energy of the
sun
1. autotrophs and heterotrophs convert glucose to
ATP and use the ATP for energy
2. any glucose not used by the autotrophs right away
is stored as starch
3. when autotrophs are consumed by heterotrophs,
the starch is broken down into glucose
4. glucose is broken down to release energy in the
process of CELLULAR RESPIRATION
38
Cellular Respiration
*** All organisms rely on cellular respiration for the energy
they need to carry out life functions.
I.
Cellular Respiration
A. process of getting ATP molecules from glucose
B. usually occurs in the mitochondria
II. 2 types of cellular respiration: Aerobic and Anaerobic
A. Aerobic respiration  requires oxygen
1. produces 36 ATP molecules from each glucose
molecule
2. has 3 distinct phases:
a. glycolysis
glucose
2 pyruvate + 2 ATP
b. Krebs Cycle
pyruvate Acetyl-CoA
Krebs Cycle
CO2 + NADH + FADH2 + ATP
 NADH and FADH2 are energy storing molecules.
Since you get 2 pyruvate from each glucose, the
Krebs cycle gets 2 more ATP.
*** So far, glycolysis and the Krebs cycle have gotten 4 ATP.
3. Electron Transport: transfers energy in the
electrons of NADH and FADH2 to ATP
a. this is the part of aerobic cellular respiration
that requires oxygen
b. electron transport generates 32 ATP molecules
**Aerobic respiration generates a total of 36 ATP molecules.
39
B. The other type of cellular respiration is anaerobic
respiration (also known as fermentation).
1. releases energy from food molecules in the
absence of oxygen
2. 2 types of anaerobic respiration:
a. alcoholic fermentation
b. lactic acid fermentation
3. In both types of anaerobic fermentation, only 2
ATP molecules are made from each molecule of
glucose.
C. Alcoholic Fermentation – Steps
1. glycolysis (just as in aerobic respiration)
glucose
2 pyruvate + 2 ATP
2. pyruvate
ethanol + CO2
This process is used to raise bread, make wine, and brew
beer by using yeasts which perform alcoholic
fermentation.
D. Lactic Acid Fermentation
1. Animal cells can’t perform alcoholic
fermentation, but some animal cells can convert
pyruvate to lactic acid.
Example: muscle cells switch to anaerobic
respiration when there isn’t enough O2 from
breathing, such as during strenuous exercise.
Muscle fatigue and soreness is from a build up of
lactic acid.
40
2. Steps of Lactic Acid Fermentation
a. glycolysis: just like in aerobic respiration and
alcoholic fermentation
b. pyruvate + NADH
lactic acid + NAD+
____________________________________________________
Photosynthesis and Cellular Respiration: Webbing Activity
WORD/PHRASE BANK
Kreb’s Cycle
Cellular Respiration
Electron transport
Get ATP and NADPH
Photosynthesis
Glycolysis
Alcoholic fermentation
Make glucose from CO2
Light reactions
Dark reactions (Calvin Cycle)
36
2
Lactic acid fermentation
Aerobic respiration
Anaerobic respiration (fermentation)
41
Cell Division
When a cell reaches its maximum size, the nucleus gives the
signal for cell division.
I. Cell Division
Needed for 3 major life processes:
1. growth: increased number of cells
2. repair: mending skin, blood vessels, etc.
3. reproduction
There are 2 types of cell division
1. mitosis: used for growth and repair, mitosis
produces cells that are identical to the parent cell;
parent and offspring cells have identical DNA
(genetic material)
a. used for asexual reproduction: process by
which an organism simply duplicates its
genetic material and splits into 2 separate,
identical organisms
2. meiosis: special form of cell division; produces
cells that are NOT identical to the parent cell
a. used in sexual reproduction, which produces
an offspring that has a combination of genetic
material from 2 parent organisms
b. the products of meiosis have only HALF the
amount of DNA (genetic material) found in
each parent cell
42
II. Mitosis
 process of cell division that gives 2 identical cells from
one parent cell
A. Cell Cycle
1. sequence of phases in the life cycle of a cell
2. covers the period of time from the beginning of
one cell division to the beginning of the next cell
division
3. the cell cycle has two parts:
a. interphase (growth and preparation)
b. cell division (mitosis)
B. Interphase:
1. occurs between divisions
2. during interphase, the cell produces all of the
material necessary for cell growth and for cell
division
3. Interphase – longest part of the cell cycle (90%)
4. Includes replication (copying) of the genetic
material before cell division
a. DNA is in the form of chromatin (thin, fibrous
strands) while it is being copied
C. Stages of Mitosis: Prophase, Metaphase, Anaphase
and Telophase
1. Prophase: chromatin condenses to form
chromosomes (which are made of DNA)
a. each species of organism’s chromosomes are
unique – in size, shape, number, etc.
43
b. chromosomes usually occur in pairs
examples:
all humans have 23 pairs of chromosomes
fruit flies have 4 pairs
some plants have hundreds of pairs
some molds have thousands of pairs
c. each chromosome has been copied (during
interphase) and the IDENTICAL chromosomes
are called sister chromatids
d. the sister chromatids are joined together at a
point called the centromere
sister chromatid
(each half of
the “X” is one)
chromatin
(interphase)
chromosome
(prophase)
centromere
e. also during prophase: nuclear membrane
(around nucleus) and the nucleolus disappear;
mitotic spindle forms (fibrous scaffolding inside
the cell)
44
2. Metaphase:
a. chromosomes are pulled to the center of the cell
and begin to line up in the middle
(if the cell was a globe, then chromosomes
would line up on the equator)
3. Anaphase
a. centromeres divide
b. spindle fibers start to pull the sister chromatids
apart
1. one of each pair goes to the poles of the
cell
2. complete set of chromosomes at each end
Think of chromosomes being pulled from the
equator to the North and South Poles
4. Telophase
a. 2 nuclei are formed
b. nuclear membranes form around each set of
chromosomes
c. chromosomes uncoil  chromatin
d. mitotic spindle disassembles
D. Cytokinesis – split cytoplasm
1. animal cells: cell membrane of the parent cell
starts to fold inward to the center until 2 cells are
formed from pinching the parent cell in half
45
2. plant cells: a cell plate forms in the middle of the
cell
a. cell plate consists of a double membrane
b. a new cell wall forms between the double
membrane of the cell plate
c. the double membrane remains and forms part
of the cell membrane of the 2 new cells
____________________________________________________
Vocabulary for Meiosis
Gene: section of DNA that controls a particular trait or
characteristic (ex. eye color)
Chromosome: lots of DNA condensed; each chromosome
contains lots of genes
Homologous chromosomes: same length, size, and shape;
code for the same traits but might have different versions of
the genes for these traits
Example: 2 homologous chromosomes carry the code for
eye color
 one chromosome might have the gene for blue
eyes while the other chromosome has the gene
for brown eyes
 same traits (eye color), different versions (blue, brown)
Our 23 pairs of chromosomes are 23 homologous pairs (46
chromosomes).
46
Diploid: di=2 ; genes are in pairs and therefore,
chromosomes are in pairs (2 sets of chromosomes)
Human cells are normally diploid: chromosomes are in
pairs (23 pairs).
Haploid: half of the normal number of chromosomes
Humans: diploid
 23 pairs  46 chromosomes
haploid  not pairs  23 chromosomes
Symbols:
n = number of sets of chromosomes
2n = diploid, 2 sets of chromosomes
1n = 1 set of chromosomes
47
Meiosis
1. Called reduction division because it reduces the number
of chromosomes by half
2n
(diploid)
meiosis
1n
4n
(haploid)
(tetraploid)
6n
meiosis
2n
(haploid)
meiosis
3n
2. Meiosis is used in sexual reproduction.
3. Results in 4 new haploid cells, called gametes.
4. Used for gametogenesis (process of making gametes)
Two types of gametogenesis:
1. spermatogenesis : process of making sperm
2. oogenesis: process of making eggs
48
Homologous Chromosomes
Further Explanation
 Homologous chromosomes are the same length, size, shape, and code
for the same TRAITS.
 The location of these traits is the same. On the diagram below,
locations are indicated with a solid black line on the chromosome.
 However, the specific GENES for these traits can be different or it can
be the same.
 Homologous chromosomes are NOT IDENTICAL. Sister chromatids
are identical.
 In the diagram below, notice that the TRAITS are written in green,
while the GENES for those traits are written in blue.
TRAIT TONGUE ROLLING
GENE  ROLLING
TRAIT  THUMB SHAPE
GENE  HITCHHIKER’S
TRAIT  EYE PIGMENT
GENE  NO PIGMENT
TRAIT  TONGUE ROLLING
GENE  NONROLLING
TRAIT  THUMB SHAPE
GENE  HITCHHIKER’S
TRAIT  EYE PIGMENT
GENE  NO PIGMENT
49
Structure of DNA
Remember: genes control certain traits, genes are sections of
DNA
I.
Structure of DNA (deoxyribonucleic acid)
A. Made of nucleotides
1. nucleotides have 3 main parts
a. sugar (deoxyribose)
S
b. phosphate group
P
c. nitrogenous base
2. 4 different nitrogenous bases can be used in a
nucleotide
a. adenine (A)
b. guanine (G)
c. cytosine (C)
d. thymine (T)
B. Watson and Crick – 1953 (published)
1. double helix shape (twisted ladder)
2. formed by 2 strands of nucleotides linked together
a. sides of the ladder are sugar and phosphate
b. “rungs” of ladder are 2 bases bonded together
***** Adenine always bonds with Thymine!
***** Cytosine always bonds with Guanine!
50
DNA
S
S
P
P
S
S
P
P
S
S
P
P
S
S
P
P
S
S
Adenine =
Guanine =
Thymine =
Cytosine =
Four Nitrogenous Bases
Nucleotide = sugar, phosphate, base
4 different nucleotides:
S
S
P
P
S
S
P
P
51
Names and Dates: Supplement to DNA Notes
 Watson, Crick and Maurice Wilkins received the Nobel prize in
1962 for their work on DNA structure and how the DNA molecule
can function to carry genetic information.
 February 28, 1953: Crick announces in the English pub “The
Eagle” that he has found “the secret of life.” Watson and Crick
published their work later in 1953.
 Rosalind Franklin:
1. She worked in the same area of Cambridge University that
Watson and Crick did but was in a different college
2. She performed research on the DNA molecule using X-ray
crystallography to take pictures; this research was the
basis of the double helix shape to DNA that Watson and
Crick are so famous for discovering. The idea of a helical
shape for DNA was all Rosalind’s. Without her work,
Watson and Crick would probably have not figured out
the DNA molecule before anyone else.
3. She did not like to share her work and her research was
“stolen” by the Watson/Crick/Wilkins lab (they went in
and examined everything without her permission),
including the famous “Photo 51.”
4. She was never acknowledged for her contribution to the
structure of DNA until Watson described her as a horrible
person in his book “Double Helix” (published 1968).
Everyone who was familiar with the DNA story objected
and the fact of Rosalind’s work being so important was
brought to the public’s attention.
52
5. She died at age 37 in 1958, before Watson publishes his
book and before the Nobel Prize is awarded. She was not
mentioned.
 Maurice Wilkins:
Ran the lab that Watson and Crick worked in; oversaw most of
their work; received the Nobel Prize with Watson and Crick in
1962
 Alfred Nobel:
Was a major business man in mid to late 1800’s; invented
dynamite and made his huge fortune from it; his brother died
and a newspaper printed Alfred’s obituary by accident and
called him the “merchant of death” (dynamite killed a lot of
people in demolition accidents); Alfred hated the thought of his
legacy being such a terrible one so when he died he left most of
his money for the establishment of the Nobel Prizes; it’s the
highest award a person can receive and covers lots of different
categories (literature, physics, medicine, peace...)
 Chargaff:
1. He studied DNA and analyzed how much thymine,
cytosine, adenine and guanine were in each sample. He
found that the amounts of thymine and adenine were
always equal, and the amounts for cytosine and guanine
were always equal.
2. Chargaff figured that adenine and thymine bond together
as do cytosine and guanine. The result was Chargaff’s
Rule:
A=T
and C = G
53
I.
DNA Replication
A. very important that DNA be able to copy itself
1. needed for mitosis and meiosis
2. process of DNA copying itself is called replication
B. Steps of Replication
1. DNA double helix unzips so that the 2 strands of
DNA are separated
 each separated strand will be a pattern for a
new strand of DNA
2. New strands of DNA are formed from single
nucleotides in the nucleus
 called free nucleotides
*3. DNA polymerase (an enzyme) matches the bases
on the parent strand (the original, unzipped part)
one by one with the new bases of free nucleotides
4. Strong sugar-phosphate bonds form between
nucleotides that are next to one another, creating a
new “backbone"
 eventually 2 new double helixes are formed,
having 1 parent strand and 1 new strand
54
I.
DNA and RNA
A. Both DNA and RNA (ribonucleic acid) are nucleic
acids
1. there are structural differences between them
DNA
Double stranded
RNA
Single stranded
Base pairs:
A–T
C–G
Base pairs:
C–G
A–U
U=uracil; replaces thymine
Deoxyribose is the sugar
Ribose is the sugar
2. RNA is used for making proteins
a. mRNA – messenger RNA
used to send information from DNA to the
ribosome
b. tRNA – transfer RNA
used to match mRNA with the right amino acids
for making proteins (remember – proteins are
made of amino acids strung together like the
beads of a necklace)
II. Protein Synthesis
A. protein synthesis is the process by which proteins are
made; it has 2 parts: transcription and translation
55
B. transcription: genetic information from a strand of
DNA is copied into a strand of mRNA
transcribe means to copy
Steps in Transcription:
1. an enzyme separates (unzips) a section of
DNA
2. unattached RNA nucleotides are linked with
the matching bases on the DNA strand to
form a molecule of mRNA
3. after a section of DNA is transcribed, the next
section is exposed (unzipped) and the process
repeats until DNA signals mRNA synthesis to
end
C. In prokaryotes, mRNA goes right to the ribosome for
translation to begin
In eukaryotes, the mRNA is first spliced inside the
nucleus.
1. splicing: removing extra parts of mRNA that
aren’t needed
After the mRNA has been spliced, it leaves the
nucleus and travels to the ribosome for translation.
D. Translation: process of converting the information in
the mRNA to a chain of amino acids (protein)
1. in the cytoplasm, one kind of amino acid is
attached to each tRNA; a section of mRNA is
attached to a ribosome
56
2. tRNA’s being amino acids to the ribosome,
and the amino acids are added one at a time
to the growing chain (tRNA transfers amino
acids to the ribosome)
 Each tRNA anticodon pairs with a
complementary mRNA codon, making sure
that amino acids are added in the coded
sequence
3. codon – 3 base section of mRNA; most carry
a code for a specific amino acid
example: UCG codes for tryptophan
anticodon – sequence of 3 bases found on
tRNA; each tRNA has only ONE anticodon
which complements a specific mRNA codon
 Anticodons and codons fit like plugs into a
socket.
4. several codons on mRNA have a different
purpose  they don’t code for regular amino
acids; instead, they are start and stop codons
which signal a ribosome to either start or stop
translation. They are located at the
beginning and end of an mRNA code for a
particular protein.
5. Codes for amino acids are universal for all
forms of life. They are the same for mice,
bacteria, and all other living organisms, even
viruses.
57
Genetics
I. Genetics
A. genetics: scientific study of heredity
1. we have known for centuries that traits are
passed from parents to offspring
2. we didn’t know how the traits were
determined
B. recall chromosomes and cell division
1. chromosomes are replicated and distributed
to daughter cells
2. reproduction requires cell division and
chromosome replication
3. we now know that traits are passed from
parents to offspring in these chromosomes
 But the relationship between chromosomes
and traits was not always understood
II. Gregor Mendel (1822 – 1884) “Father of Genetics”
A. Facts:
1. Austrian monk
2. Began his work in the 1860’s
3. Used mathematics in his study of the garden pea
plant
 During Mendel’s time, most people thought that
traits were a result of a blending of the parents’
traits. Mendel showed something different.
III. Mendel’s Work
A. worked for more than 8 years on his pea plant
experiments, using more than 20,000 plants!
58
1. chose the pea plant for 3 reasons:
a. structure of the pea flower (more later)
b. presence of distinctive traits
c. rapid reproductive cycle
2. these characteristics allowed Mendel to isolate and
control variables, and to produce observable
results that he could duplicate
B. Structure of the Pea Flower
1. easy to self-fertilize (pollen from the anther
fertilizes the pistil of the same plant)
2. through self-fertilization, able to get purebred
plants
a. purebred: any organism that receives the
same genetic traits from both of its parents
example: if you get the gene for attached
earlobes from your mom AND from your
dad, you are purebred for attached earlobes
(both copies of the gene are the same)
3. the pea flower structure was also good for crossfertilization (fertilization using 2 different plants)
a. produced hybrids: organisms that receive
different forms of a genetic trait from each
parent
example: if you get the gene for attached
earlobes from your dad and the gene for free
earlobes from your mom, you are a hybrid
for earlobe shape
4. Mendel studied 7 different traits in the garden pea
plant, all of which were easy to observe
59
a. each of these traits has only 2 distinct forms
(rather unusual)
examples:
pea pods are either yellow or green
pea plant stems are either tall or short
 never an “inbetween” like medium height
The Experiments
I.
Mendel began by using 2 different groups of purebred
plants  examining pea color
A. he called this generation (the 2 purebred plants) the
parental generation , or P generation
 the P generation was either purebred yellow or
purebred green
1. He crossed these 2 parental plants to produce
offspring, called the F1 generation (“F” stands for
filial, which means offspring)
P
purebred green X
purebred yellow
F1
**2. The F1 generation all had yellow peas
3. Next, Mendel allowed the F1 generation to selffertilize, producing the F2 generation
4. In the F2 , ¾ of the plants had yellow peas and ¼ of
the plants had green peas
60
B. What had Mendel expected to happen?
1. The blending hypothesis would predict greenishyellow (or yellowish-green) peas
2. Instead, the F1 generation plants all had yellow
peas  no green peas, even though one of the
parents had green peas
 But when the F1 self-fertilized, the green peas
came back in the F2 generation!
The F2 generation had 75% plants with yellow
peas and 25% of plants had green peas
**** Ratio – 3 plants w/ yellow peas : 1 plant w/ green peas
C. Mendel repeated the experiment for the other 6 traits
1. for each trait, he observed the same results in the
F1 generation:
 all of the F1 plants showed only one form of the
trait
ex.
P
purebred tall X
purebred short
F1
all tall plants
____________________________________________________
P
F1
purebred purple flowered X purebred white flowered
all purple flowered plants
61
2. Mendel defined each form of the trait as either
dominant or recessive.
 The dominant form appeared in the F1
generation, the recessive form did not appear
in the F1
3. In the F2 generation of his experiments, Mendel
always got 2 types of plants – 75% were the
dominant form, 25% showed the recessive form
*see diagram of Mendel’s experiments through the F2
II. Mendel’s Conclusions
A. Mendel’s experiments proved that the blending
hypothesis was wrong
1. never observed pea plants with mixtures of the 2
forms of the trait
2. Mendel reasoned that forms of a trait must remain
separate in offspring
B. Mendel hypothesized that each trait is controlled by a
distinct “factor”
1. since there were 2 forms of each trait, Mendel
realized that there must be at least 2 forms of each
factor
2. He reasoned that for every trait, a pea plant must
carry a PAIR of factors which could affect each
other; When a trait is inherited, the offspring
receives one factor from each parent.
C. We now know that Mendel’s “factors” are genes
1. recall: most organisms have 2 copies of every gene
and chromosome (homologous chromosomes) 
one copy from each parent
62
2. We refer to the different forms of Mendel’s factors
as alleles
Allele: distinct form of a gene
 If an organism has 2 different alleles for a trait, only one is
expressed or visible
Example: A person has an allele for free earlobes and an
allele for attached earlobes, yet that person’s earlobe shape
is just free. (only one of the alleles is expressed)
 Dominant allele: form of a gene that is fully expressed
when 2 different alleles are present
 Recessive allele: form of a gene that is NOT expressed
when paired with a dominant allele
Mendel published an account of his experiments in 1866. His
work was unrecognized for 37 years.
Rediscovering Mendel
Late 1880’s : a new staining technique allows chromosomes
to be viewed for the first time
Early 1900’s : Mendel’s work is rediscovered
I.
Walter S. Sutton – 1903
A. Sutton was observing stained cells through a
microscope and realized that chromosomes behaved
like Mendel’s factors
63
B. Developed the Chromosomal Theory of Heredity
which states that the material of heredity is carried
by the genes in chromosomes (remember – didn’t know
that this “material of heredity” was DNA until the late
1940’s-early 1950’s, and didn’t know the structure of
DNA until 1953)
C. To explain and use the theory, a system of terms and
symbols was developed.
WE USE LETTERS TO REPRESENT ALLELES.
But, how do you know which letters to use?
 Use the same letter for both forms of the trait because
both dominant and recessive alleles are for the same
trait. We just use capital and lowercase forms of the
letters to show the difference.
 The dominant allele always determines the letter – the
first letter of the dominant form of the trait is chosen and
the dominant allele always uses an capital letter
 The recessive allele always gets a lowercase letter.
Ex. pea color
Yellow is dominant, green is recessive.
We use the letter “Y” because it is the first letter in
the dominant form (Yellow).
 The allele for yellow peas is represented by an
capital letter “Y”
 The allele for green peas is represented by a
lowercase letter “y”
64
D. Genotype and Phenotype
1. genotype: the genetic make-up of an organism
a. includes both genes in a homologous pair of
chromosomes
examples:
a plant purebred for yellow peas: __YY__
a hybrid plant for pea color:
_ Yy___
a plant purebred for green peas: __ yy___
2. phenotype: outward expression or appearance of a
trait
example:
the hybrid with genotype Yy has the phenotype
yellow peas (recall dominance)
3. Describing genotypes
a. homozygous: the 2 alleles in a gene pair are the
same
examples: YY and yy
“Mendel’s purebred plants were homozygous for pea color.”
b. heterozygous: the 2 alleles for a trait are
different
examples: Gg, Yy, Pp
“Mendel’s hybrid plants were heterozygous for pea color.”
65
Mendel’s Laws
Mendel’s Laws
A. basic rules of inheritance
1. there are exceptions (more on that later)
2. many traits do follow Mendel’s laws (called
Mendelian traits)
B. The Law of Segregation
“Each pair of genes segregates, or separates, during meiosis.”
1. Because of segregation, half of an organism’s
gametes contain one gene from a homologous pair
and half of the gametes contain the other gene.
C. The Law of Independent Assortment
I.
“Gene pairs segregate into gametes randomly and independently
of each other.”
1. Mendel studied the inheritance of 2 traits at the
same time
Example: pea color and pea shape
P
purebred yellow round peas
Genotype: ____YYRR__
X
purebred green wrinkled peas
Genotype: __yyrr____
F1
all plants had yellow round peas
(self fertilized to get F2)
F2
All possible combinations were produced:
Yellow round peas
Yellow wrinkled peas
Green round peas
Green wrinkled peas
66
 The association of traits in a parent didn’t seem to
matter.
 yellow wasn’t always with round
 green wasn’t always with wrinkled
We could get combinations that were different from the
parents.
D. Law of Dominance
“The dominant allele is expressed and the recessive allele can
be hidden.”
1. a recessive allele is expressed only when an
organism has NO COPY of the matching
dominant allele
Example: plant heterozygous for flower color
Recall: purple is dominant over white
Allele for purple flowers: ___P____
Allele for white flowers: ___p____
Genotype: ____Pp___
Phenotype: ___purple flowers____
67
Probability:
A. Scientists use probability to predict the phenotypes and
genotypes of offspring in breeding experiments.
1. When you use fractions, percents, ratios, or decimals
to predict the outcome of an event, you’re measuring
probability.
2. In biology, Punnett squares are used to help predict
the results of breeding experiments
a. grid to organize genetic information
b. shows probabilities
B. A monohybrid cross (one trait, both parents are
heterozygous) will give a 3 dominant : 1 recessive ratio in
the offspring for Mendelian traits.
Example:
P
tall
Tt
F1
T
t
X
T
TT
Tt
3 tall : 1 short
t
Tt
tt
tall
Tt
Key:
T= allele for tall
t = allele for short
68
Genetics Problem Set-Up
KEY
(symbol here)
(symbol here)
P ♣
= allele for (dominant version of trait here)
= allele for (recessive version of trait here)
phenotype of 1st parent
genotype of 1st parent
F1
♣
(if applicable) -
X ♣
phenotype of 2nd parent
genotype of 2nd parent
♣
Answer to the question in a box
Also – If the sex of each parent is known (male, female) the
symbols for the sex must be included in the parental
generation and in the Punnett square. (see cloverleaf marks)
Male:
Female:
69
Answer Set-Up for Certain Genetics Problem Questions
If a genetics problem asks you to “list (give, name) the genotypes
and phenotypes of the offspring” there is a specific way to arrange
your answer. So that it is clear in your answer as to what is a
genotype and what is a phenotype, you must make a chart.
For example, if you are asked to list the genotypes and phenotypes
of the offspring for the following Punnett square:
T
t
T
TT
Tt
t
Tt
tt
then your answer would be:
genotypes
phenotypes
TT
tall
Tt
tall
tt
short
Also, if you are asked to give the “genotypic and phenotypic
ratios of the offspring” you must identify which ratio is
which. Using the same Punnett square from above, you
would write:
Genotypic ratio - 1 TT : 2 Tt : 1 tt
Phenotypic ratio - 3 tall : 1 short
70
Notice that each is labeled and colons separate each part.
Practice Single Trait Inheritance (STI) Problems
1. Cross a homozygous tall plant with a short plant. What
percentage of the offspring will be tall?
2. Cross a plant hybrid for flower position with a plant that
is purebred dominant for flower position. What fraction of
the offspring will be heterozygous?
3. Cross two heterozygous plants using the trait pea shape.
What percentage of the plants will be recessive?
71
A dihybrid cross (2 traits, both parents are completely
heterozygous for both traits) will result in a 9:3:3:1 ratio in
the offspring where:
9 offspring will have both dominant traits
3 have one dominant and one recessive trait
3 have one dominant and one recessive trait
1 has both recessive traits
(remember – works for Mendelian traits only)
Example:
P
purple tall
PpTt
X purple tall
PpTt
Key:
P = purple
p = white
T = tall
t = short
F1
PT
Pt
pT
pt
PT
PPTT
PPTt
PpTT
PpTt
Pt
PPTt
PPtt
PpTt
Pptt
pT
PpTT
PpTt
ppTT
ppTt
pt
PpTt
Pptt
ppTt
pptt
9 purple tall : 3 purple short : 3 white tall : 1 white short
72
How to Set Up a Double Trait Inheritance Problem
The hard part is getting the gametes from each parent to
make up the top and left side of your Punnett Square. Follow
the pattern:
The left side tells you
which letter to take
from the alleles for
the first trait.
1st 1st
1st 2nd
2nd 1st
2nd 2nd
The right side tells
you which letter to
take from the alleles
for the second trait.
So, following the pattern, here are the gametes you would get
from a parent with the genotype AaRr. Note that “Aa” are
the alleles from the first trait and that “Rr” are the alleles for
the second trait.
AaRr
1st 1st
1st 2nd
2nd 1st
2nd 2nd
AR
Ar
aR
ar
Now you take these combinations to
begin setting up your Punnett
square, as is shown below.
AR
To get the
gametes that go
down this side,
you do the same
procedure only
use the other
parent.
Ar
aR
ar
73
Shortcuts for Punnett Squares
You only need one of each different gamete from each parent for
your Punnett squares. If you have 2 or more copies of the exact
same gamete FROM THE SAME PARENT, eliminate the
duplicates.
For example, let’s say your crossing the parents RRGg and RrGG.
Use the 1st 1st, 1st 2nd, etc. pattern to get all the possible gametes.
1st 1st
1st 2nd
2nd 1st
2nd 2nd
RRGg
RrGG
RG
Rg
RG
Rg
RG
RG
rG
rG
Some of the gametes are the same for the same parent, so cross them
out.
1st 1st
1st 2nd
2nd 1st
2nd 2nd
RG
Rg
RG
Rg
RG
RG
rG
rG
Now, use the remaining gametes to make your Punnett
square. The blue shows the resulting offspring.
RG
Rg
RG
RRGG
RRGg
rG
RrGG
RrGg
74
Please note the following about double trait problems:
 You either have to cross out ALL of the duplicates or NONE of
them for a double trait problem to work out correctly.
 You will NEVER have 3 gametes from a parent in a double
trait problem. If you do, you either crossed out a gamete you
shouldn’t have, or you didn’t cross out ALL of the duplicates.
 Only a completely or fully heterozygous parent will get you 4
different gametes, which is the highest number of gametes you
can have for a double trait problem.
75
Human Blood Types: Codominance and Multiple Alleles
Codominance: both alleles in the heterozygous genotype
express themselves fully
Multiple alleles: three or more alleles for a trait are found in
the population
Blood Type Alleles:
IA – produces antigen A
IB – produces antigen B
i – produces no antigens
Note: replace “produces”
with “allele for” to get the
key for all blood types
problems.
IA and IB are not dominant over each other. The allele i is
recessive to IA and IB.
Genotype
Phenotype
IAIA or IAi
Type A blood
IBIB or IBi
Type B blood
I AI B
Type AB blood
ii
Type O blood
Blood Types:
If you are Type A, you have antigen A on your red blood
cells. You also have antibody B in your blood plasma.
Antigen: a type of carbohydrate attached to RBC’s
Antibody: part of your body’s defense system
 antibody B “attacks” antigen B
76
If you are Type B, you have antigen ___B__ on your
RBC’s and antibody __A__ in your blood plasma.
If you are Type AB, you have antigen __A__ and antigen
__B__. (That’s codominance – both IA and IB are
expressed.) You have no antibodies if you’re type AB.
Why?
If you are Type O, you have no antigens on your RBC’s,
and you have antibodies A and B.
NOTE: Only the antigens are donated, not the antibodies.
TYPE
A
B
AB
O
Can Donate To:
A, AB
B, AB
AB
O, A, B, AB
Can Receive From:
O, A
O, B
O, A, B, AB
O
Type AB is called the universal recipient, and Type O is
called the universal donor. Why?
Reference Chart: Antigens and Antibodies
Antigen A
Antibody A
Antigen B
Antibody B
Type A
Type B
Type B
Type A
Type AB
Type O
Type AB
Type O
77
Blood Type Problems
1. What’s the probability of a woman with type AB blood
and a man with type O blood having a child with type A
blood?
2. Cross a man heterozygous for type A blood with a woman
with type AB blood. Give the genotypic and phenotypic
ratios of their offspring.
3. A man with type A blood and a woman with type B blood
have a child with type O blood. Give the genotypes of the
parents and the child and show a Punnett square for the
cross.
78
Mutations
Mutation: a random change in the sequence of nucleotides
in DNA
mutagen: a factor in the environment that causes a
mutation
examples:
radiation (nuclear, X-rays)
chemicals (tobacco)
UV rays (can cause skin cancer)
2 types of mutation:
1. chromosomal mutations: involve entire chromosome
2. gene mutations: involve individual genes
Chromosomal Mutations:
1. deletion: a piece of a chromosome breaks off and is
lost
2. duplication: extra copy of part of a chromosome
 Usually, chromosomal mutations have huge effects. Most
deletions are lethal.
Gene Mutations:
1. frameshift mutation: nucleotides are lost or gained,
disrupting the codon sequence
Pat the bad cat. (delete 1 letter)
Ptt heb adc at  nonsense!
So if you’re reading codons and one base is lost, it can change
all the amino acids that are coded for after the deletion. It
could give an entirely different protein, or no protein at all.
79
2. Point Mutation: a change that occurs in only one
nucleotide
Ex. DNA has bases ATA mutation ATC
When the DNA is transcribed to mRNA, the mutation
can affect what amino acid is coded for.
DNA:
mRNA:
codes for:
ATA
UAU
tyrosine
mutation
ATC
UAG
STOP codon
80
1.
2.
3.
4.
Mutations: The Good, The Bad, and The Ugly
Sometimes mutations can have almost no effect on an
organism.
Sometimes mutations can kill an organism.
Sometimes mutations can be harmful to an organism but
not kill it.
Sometimes mutations can be helpful to an organism,
giving it a new gene that is an advantage.
examples:
 a mutation in a deer thaqt results in
better hearing
 a mutation in a rabbit that gives it thicker
fur in the winter
 a mutation in a squirrel that gives it
bigger mouth pouches to carry food
How is each one of these mutations helping the
organism to survive?
81
Incomplete Dominance
Incomplete dominance:
genetic inheritance in which neither allele is completely dominant or
recessive; the heterozygous condition produces a phenotype that is
intermediate between the alleles
Example: In snapdragons, there are 2 alleles for flower color: C1 is
the allele for red flowers and C2 is the allele for white flowers.
P
homozygous red
X
homozygous white
C1 C1
C2 C2
F1
C1
C1
C2 C1 C2
C1 C2
C2 C1 C2
C1 C2
KEY:
C1 -- red
C2 -- white
All F1 offspring are
C1 C2
which gives the phenotype of
PINK flowers. (Note: snapdragons & four o’clock flowers use the
same alleles).
Another example of incomplete dominance is sickle cell anemia in
humans. Homozygous recessive produces the disease, homozygous
dominant has no disease. If you have the disease, your red blood
cells are sickle shaped under low oxygen conditions and can’t carry
oxygen very well. They also clog up blood vessels, cutting off the
blood supply to different areas of the body.
People with the heterozygous ( HbS HbA ) genotype for sickle cell
anemia do NOT have the disease. Only a few of their RBC’s are
sickle shaped and the normal cells carry enough oxygen. However,
heterozygotes have an advantage – they are immune to the disease
malaria, which is spread by mosquitoes and is often fatal if not
treated properly.
82
Sickle-Cell Anemia and Hemoglobin
Incomplete Dominance in terms of Red Blood Cell Shape
Codominance in terms of Hemoglobin
Organismic
Phenotype
Genotype
Sickle-Cell
Trait
HbSHbA
(heterozygous)
Hemoglobin Types
Present
S and A
Since both forms of hemoglobin
are
(few RBC’s sickle shaped
but only under low oxygen - since
of
this is an intermediate, RBC shape in
sickle cell is an example of incomplete
dominance)
Sickle-Cell
Anemia
present, in terms of hemoglobin,
sickle cell is actually an example
codominance.
HbSHbS
S
HbAHbA
A
(RBC’s are sickle shaped)
Normal
(RBC’s never sickle shaped)
Remember: Sickle-cell trait and sickle-cell anemia are NOT the same thing.
Sickle-cell trait has a few red blood cells that become sickle shaped but only under low
oxygen levels. However, people with sickle cell trait (heterozygous) are also immune to
malaria. This is a huge advantage for populations existing where malaria is rampant.
It is also the reason why sickle cell anemia is still common in these same populations. In
some areas of West Africa, as much as 40% of the population is heterozygous (sicklecell trait). It would be a disadvantage to be heterozygous in areas of the world where
malaria is not a threat, since being heterozygous introduces the possibility of passing on
sickle-cell anemia to children and future generations.
Having sickle-cell anemia affects the general health of a person in a lot of ways. For a
flow chart illustrating these devastating effects, examine the other side of this paper.
It is important to note that while sickle-cell trait and sickle-cell anemia are extremely
rare in Caucasian populations, it is not impossible for a Caucasian person to have either
of these.
83
Sex-Linked Traits
Sex-linked traits:
traits that are controlled by genes located on the X chromosome
Our understanding of sex-linked traits came from studying the fruit
fly. Sex is determined the same way in fruit flies as it is in humans
 _____XX_____ = female
_____XY______ = male
___Thomas Hunt Morgan_______ : year: ___1909____ : While
studying fruit flies, he noticed a male fly with white eyes (red eyes is
the normal phenotype). He crossed this male with a red eyed
female. All of the F1 had red eyes, showing that ___red_______
eyes were dominant. So far, the cross fit the normal pattern.
P
red eyed female
_____RR_____
F1
X
white eyed male
_____rr______
R
R
r
Rr
Rr
r
Rr
Rr
KEY:
R = red eyes
r = white eyes
Note: This cross
later turned out to
be incorrect!!
All F1 flies have the genotype _______Rr______ and the
phenotype _________red eyes________.
Morgan crossed the F1, expecting the 3:1 ratio that a monohybrid
cross would normally give
(3 ____red eyed________ : 1 ________white eyed________). He got
that ratio, but with a twist. All of the white eyed flies were males!
Morgan explained that his results were from the gene for eye color
being located on the ____X___ chromosome. If you look at his
complete experiment through the F2, you can see how it works out.
With sex-linked traits, we also keep track of the sex chromosome in
addition to the gene for the trait. Check out the revised key.
84
P
red eyed female
X R XR
X
XR
XR
Xr
X R Xr
X R Xr
Y
XR Y
XR Y
F1
Key:
XR -- gene for red eyes
Xr -- gene for white eyes
Y -- males, no gene for trait
white eyed male
Xr Y
F1 are all ___red eyed_____ for phenotype, with the genotypes
___ XR Y ___(Male) or ___ XR Xr (Female).
(Remember, to get the F2, cross the male and female F1.)
red eyed male
___ XR Y __
F2
XR
Xr
X
XR
Y
XR XR
XR Y
X R Xr
red eyed female
___ XR Xr
Xr Y
# of offspring Genotypes
Phenotype
Sex
R
R
___1__
__ X X __
_____red eyes________
female
R
___1__
__ X Y___
_____red eyes________
male
R
r
___1__
__ X X __
_____red eyes________
female
___1__
___ Xr Y __
_____white eyes______
male
In sex-linked traits, there is no corresponding gene on the Y
chromosome in males, so whatever gene is on the X chromosome is
expressed, whether it is dominant or recessive.
85
The recessive condition of sex-linked traits is mostly found in males
(although it is still possible to have a female with the recessive
condition). Why is this true?
Male only need one recessive allele for the recessive form to be
expressed.
Females must have TWO recessive alleles.
There are several sex-linked genes in humans. Colorblindness,
Duchenne Muscular Dystrophy, and Hemophilia (a disease in which
a person’s blood has extreme difficulty in clotting) are a few of
them. The genes for these diseases are recessive. However, the
symbols are different. For hemophilia, we use the symbols XH -normal clotting and Xh – hemophilia.
Cross a man with hemophilia with a woman who is heterozygous.
Give the genotypes and phenotypes of the possible children,
including the sex of each possibility.
P
hemophilia
Xh Y
F1
Xh
*
no disease
XH X h
Y
XH XH Xh XH Y
Xh Xh Xh
Xh Y
Geno.
Pheno.
Sex
XH Xh
no disease
female
XH Y
no disease
male
X h Xh
hemophilia
female
Xh Y
hemophilia
male
KEY:
XH – no disease
Xh - hemophilia
Y – no gene
86
Sex – Linked Traits: Problem Keys for Common Diseases
Hemophilia:
Duchenne Muscular Dystrophy:
XH – no disease
Xh – hemophilia
Y – no gene
XD - no disease
Xd – DMD
Y – no gene
Colorblindness:
XC – no disease 
Xc – colorblind
Y – no gene
Please make sure there is a physical
difference between your capital “C”
and your lowercase “c” !!!
Hypophosphatemia: 
XH – hypophosphatemia
Xh – no disease
Y – no gene
Note that the allele for this disease is
is dominant, yet the alleles for all of
the other diseases listed above are
recessive!
Don’t forget eye color in fruit flies:
XR – red eyes
Xr – white eyes
Y – no gene
87
Sex-Limited Trait
Sex-limited traits:
Traits that are only expressed in the presence of sex hormones and
are only observed in one sex or the other
_
Sex-limited traits are controlled by genes located in the autosomes
(non-sex chromosomes). Although both males and females carry
these genes, they are only expressed in one sex. Because you need
large amounts of the proper sex hormone for the genes to be
expressed, most sex-limited traits are not expressed in children.
Examples: In many birds, male plumage is more colorful than
female plumage. In humans, beard growth in men is a sex-limited
trait as well as milk production in women.
GENE + HORMONE = SEX LIMITED TRAIT
Sex-Influenced Traits
Sex-influenced traits:
Traits expressed in both sexes, but they are expressed differently __
Example: Baldness
1. In the presence of male sex hormones, the allele for
baldness is dominant.
2. Female sex hormones cause the allele to be recessive. A
woman may lose hair if her genotype is
homozygous recessive.
Polygenic Traits
Polygenic trait:
Trait that is controlled by more than one gene
 polygenic traits are especially prevalent in genes that control
body shape
or form .
Inheritance of polygenic traits can be very complicated.
Example: parakeet color  see handout
__
88
Some human traits that are considered polygenic:
a. skin color (numerous genes control the amount of
melanin in the skin)
b. height
Nondisjunction
Nondisjunction:
“not coming apart”
Recall from meiosis that during anaphase, the chomosomes are
pulled apart to opposite ends of the cell. If this doesn’t happen
properly during oogenesis or spermatogenesis, the egg or sperm will
end up with too few or too many chromosomes.
Example:
X
X
X
X
Metaphase II
8 chromosomes
4 pairs of homologous
chromosomes
Anaphase II
5 chromosomes
(vs. normal 4)
3 chromosomes
(vs. normal 4)
89
Many human genetic disorders are a result of nondisjunction.
1. Down’s Syndrome: trisomy 21  there are ____3____ copies
of chromosome number 21 instead of the normal ____2___
copies. Some of the characteristics of people with Down’s
syndrome include:
a. reduced mental capacity (varies greatly between
individuals)
b. lack of muscle tension (“floppy” appearance,
tongue often lolls)
c. ears are placed lower on the head (often problems
with ear infections as infants)
d. larger head and facial features are closer together
e. life expectancy is greatly reduced (late twenties to
early thirties was lifespan; now closer to 40’s, 50’s)
f. often sterile, but not always
2. Turner Syndrome – “XO” – a sperm or egg is produced
without a sex chromosome; the O indicates a missing sex
chromosome
people with Turner’s syndrome are females; the sex
organs do not fully develop and therefore they are
sterile; lack secondary sex characteristics
3. Klinefelter Syndrome – “XXY” – an extra X is present from
either the sperm or the egg
people with Klinefelter syndrome are usually male,
may have reduced mental capacity, and are often
sterile; lack secondary sex characteristics
Notes on XYY Syndrome: (aka Richard Speck Syndrome )
sex: male
characteristics: tall; lanky; severe adult acne;
aggressive/violent tendencies
___
 a study done on XYY syndrome showed a proportionately larger
population of XYY males in prison than in the general population
90
Environmental Effects on Gene Expression
Gene expression can be affected by both the external environment
and the internal environment inside an organism. Phenotype is
generally a combination of genetic and environmental influences.
Example: Himalayan rabbits (temperature)
1. The rabbits are normally covered with white fur.
2. However, its ears , nose, and feet are black.
3. This pattern occurs because most of the rabbit’s body is
generally warmer than its extremities.
4. Body temperature affects the expression of genes
that code for fur color.
5. When researchers remove a patch of hair from the body
and cool the skin as new fur grows, the new fur is
_____black______. When they shave hair from the feet
or ears and keep those areas warm, the fur that grows
back is ____white_________.
Example: Japanese goby fish (social environment)
1. The goby fish can change its ___sex_____ back and forth
in response to changes in its social environment.
2. Goby fish exist in schools of many females and only a
few males.
3. If a large male goby leaves a population, a female goby
will ____become male_____.
4. If another large male enters that goby population, this
new male turns back into a female.
Example: Human height (internal environment)
 While human height is a ____polygenic_______
trait, it is also affected by the nutrients in your diet.
91
Evolution
Vocabulary
Species:
Interbreeding populations of organisms that can produce healthy,
fertile offspring
Within species, lots of variation exists.
Variation:
the differences between individual members of a population
 Variation can be dramatic (different colors of fur), it can be
subtle (slightly different diet), or it can be difficult to observe
(different hormone levels).
Many (though not all) variations are genetically determined.
The particular traits inherited by an individual organism
determine whether that organism will survive in a particular
environment.
Adaptation:
An inherited trait that increases the chances of survival and
reproduction in a particular environment; “an advantage”
Evolution:
the idea that organisms change over long periods of time
92
Theory and Evidence of Evolution
The Earth is home to millions of different organisms, each different
from the other. By examining the
fossil record
, we can see that
there were even more organisms that no longer exist. Many people
have tried to explain the origin and the diversity of life for
thousands of years.
EVIDENCE:
1. Diversity:
millions of different organisms exist on the Earth
With this diversity, each organism is well adapted to its
__environment__.
2. Geological Time Scale:
By examining ____geological formations___ and using such
techniques as ____radio-carbon dating____, we can conclude that
the Earth is 5.5 – 6 BILLION years old. This gives lots of time for
change to occur.
3. Fossil Record:
We can trace the ______ancestors___ of organisms through the
fossil record. Some organisms’ fossil history is more __complete___
than others. And using radiocarbon dating, we can date these fossils
and put them in order to see what __changes___ have taken place.
example: horse (see handout)
93
4. Homologous Structures:
traits that are similar in different species because the species share a
common ancestor
__
 Example: the human arm, whale fin, and bat wing may have
evolved from the forelimb of a common vertebrate ancestor
Notice the pattern:
1 large bone  2 smaller bones  many very small bones
 the appearance of each is different because:
these species are adapted to their particular environments
5. Vestigial Structures:
structures or characteristics that are greatly reduced in size and_
usually not used; vestigial structures are homologous with
structures in other species which suggests common ancestry with_
those species
Example: python’s leg and hip bones – reduced and not used
 These bones are remnants of structures that were used in an
ancestor.
 The python’s hip and leg bones are homologous to the hip and leg
bones of other legged reptiles, which suggests that the python is
related to legged reptiles.
94
6. Embryos :
embryos of related organisms develop in similar ways
Example: gill pouches  They form in embryos of all vertebrates;
in fish, they develop into gills, but in mammals they don’t develop at
all. Gill pouches may have been inherited from a common ancestor.
7.
DNA :
DNA is found in every living organism, without exception; the codes
for amino acids are universal
__
__
8. ATP :
all living organisms use ATP as an energy source; no exceptions
Ideas of How Evolution Happens
1. Jean Baptiste Lamarck (1809)
first person to reason that fossils of extinct organisms were the____
ancestors of those organisms living today
______
Three main parts to his hypothesis of how evolution happened:
1. Organisms constantly strive to improve themselves.
2. Principle of Use and Disuse:
The most used body structures develop, while unused
structures waste away; “use it or lose it”
95
3. Inheritance of Acquired Characteristics:
Once a structure is modified by use or disuse, the modification
is inherited by the organism’s offspring
_
Examples: if you have brown hair and dye it blond, your children
will inherit blond hair, not your natural color (brown); tattoos
 Lamarck’s hypothesis was later disproved by German biologist
August Weismann through experiments with mice.
3. Charles Darwin (b. 1809 d. 1882)
joined an around the world trip in 1831 on the HMS Beagle;
during the trip, he collected ___plant___ and ___animal____
specimens and logged countless observations
noticed the variety of species in the world and how each
different species had its own spot in its environment
Influences on Darwin:
1. Geology: from ___Charles Lyell_____
Darwin learned that geological change is an extremely slow
and uniform process
 Darwin concluded _that the Earth must be very, very old._
 Darwin reasoned that gradual geological changes over long
periods of time influence plant and animal life.
96
2. Artificial Selection:
___the selective breeding of domestic animals and crops___
ex. choosing parents to get the most desirable traits
(corn, dogs)
 Artificial selection often results in organisms that bear little
resemblance to their ancestors.
 Darwin reasoned that a selection process also occurred in
nature.
3. Thomas Malthus and Population Control
An economist, Malthus stated that:
The human population was growing so fast that the supply
of resources couldn’t possibly keep up with demand
__
Disasters such as war, diseases, or starvation limited the
growth. Darwin saw this in nature with other species. If all
of the offspring of a population survive, the population would
quickly outgrow its supply of resources.
 So not all offspring can survive.
There is always competition for _____food____,
______water____, and ______living space_____.
Example: frogs, fish, insects
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Darwin’s Theory of Evolution: Natural Selection
 In 1844 Darwin wrote a paper on his theory of evolution, but
because he knew his ideas would challenge popular beliefs, he did
not publish the paper for over 10 years. Meanwhile, another
naturalist, ____Alfred Wallace________, developed a theory similar
to Darwin’s. In 1858, both men agreed to send their papers together
to the same scientific organization. Wallace gave Darwin credit
since Darwin had the idea first.
1859 – Darwin publishes the book
“ On the Origin of Species by Means of Natural Selection__”
which gives greater detail to his theory.
Natural Selection: 5 Main Parts
1. __There is variation within populations
 there are differences between organisms, even those of the
same species
 many variations are inherited and are passed from parent to
offspring
2.
Some variations are favorable.
 if favorable, the variation improves the organism’s ability to
function, survive, and reproduce in its environment
3.
Not all of the young produced in each generation can survive.__
There’s only so much food, space, and resources to go around.
 many offspring die from disease or starvation
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4.
There is a struggle for survival.
Organisms must compete with each other for the available
resources.
5.
Those individual organisms with the favorable variations will
survive and reproduce.
“Survival of the Fittest”
 When these survivors reproduce, their favorable variations
will be passed on to their offspring.