Unit 5, 6, and 7
Difference Between Meiosis and
Mitosis!
• You need to understand the difference between mitosis and meiosis.
They’re similar, but:
• Mitosis: makes more body or SOMATIC cells.
• Meiosis: Makes more sex cells or gametes.
• Meiosis: a form of cell division that halves the
number of chromosomes when forming specialized
reproductive cells, such as gametes or spores.
– There are two stages of meiosis, Meiosis I and
Meiosis II
– In animals, meiosis produces haploid gametes or
sex cells, sperm and eggs
Formation of Haploid Cells
• Before the process of meiosis, like mitosis, the DNA
replicates.
• This makes a cell with how many chromosomes?
• There are 8 stages in Meisois, and they should
sound familiar:
MEIOSIS I:
•Prophase I
•Metaphase I
•Anaphase I
•Telophase I and cytokinesis
MEIOSIS II:
•Prophase II
•Metaphase II
•Anaphase II
•Telophase II and cytokinesis
Meiosis I
Meiosis II
Crossing-Over and Random
Fertilization
• DNA exchange during crossing over in Prophase I adds even more
recombination to the independent assortment of chromosomes,
making even MORE genetic combinations!
 Crossing-Over: a type of genetic recombination that occurs when
portions of a chromatid on one homologous chromosome are
broken and exchanged with the corresponding chromatid, increasing
genetic diversity.
•Meiosis, gamete-joining, and
crossing-over are essential to
evolution because these processes
generate genetic variation very
quickly.
•The pace of evolution is sped of by
genetic recombination!
Sexual and Asexual Reproduction
• Some organisms have two parents, other only have
one.
• Reproduction can be sexual or asexual.
• Sexual Reproduction: two parents form reproductive
cells that have one-half the number (haploid) of
chromosomes which combine to make a diploid
individual.
• Asexual Reproduction: a single parent passes copies of
all its genes to each of its offspring—no fusion of
haploid cells such as gametes.
– Clone: an organism that is genetically identical to its parent.
Hypotheses for Heredity
• Prior to Mendel’s work, people thought offspring
were a blend of their parents.
• Mendel’s work did not support the blending
hypothesis.
• Mendel concluded that each pea had two separate
“heritable factors” for each character—one from
each parent.
– When sperm and eggs (gametes) form, each receives
only one of the organism’s two factors for each
character.
– When the gametes fuse, each offspring has two factors
for each character.
Mendel’s Hypotheses
1. For each inherited
character, an
individual has two
copies of the gene—
one from each parent.
2. There are alternative
versions of genes—a
pea plant can have a
purple version or a
white version.
–
Allele: the different
versions of a gene
Mendel’s Hypotheses
3. When two different alleles occur
together—one of them may be
completely expressed, while the
other may have no observable
effect on the organism’s
appearance.
– Dominant: the expressed form of
the character
– Recessive: the trait not expressed
when the dominant form is
present.
Mendel’s Hypotheses
• 4. When gametes are
formed, the alleles for
each gene in an
individual separate
independently of one
another. Thus,
gametes carry only one
allele for each inherited
character. When
gametes unite during
fertilization, each
gamete contributes
one allele.
Mendel’s Findings in Modern Terms
• Dominant Traits: Capital letter
• Recessive Traits: lower case letter
• Pea Plants:
– Purple—Dominant: P (capital P)
• Homozygous: if the two alleles of a particular
gene are the same in an individual
• Heterozygous: if the two alleles of a particular
gene are different in an individual
Mendel’s Findings in Modern Terms
• Genotype: the set of alleles
that an individual has for a
character.
–The genes they actually
have.
• Phenotype: the physical
appearance of a character.
–How they look.
The Laws of Heredity
• The Law of Segregation: the two alleles for a
character segregate (separate) when gametes are
formed.
– This is the behavior of chromosomes during meiosis.
• The Law of Independent Assortment: The alleles of
different genes separate independently of one
another during gamete formation.
– The inheritance of one character does not influence the
inheritance of another, as long as they’re on separate
chromosomes!
Punnett Squares
• Punnett
Square: A
diagram that
predicts the
outcome of a
genetic cross by
considering all
possible
combinations of
gametes in the
cross.
Inheritance
• Dominant: If the gene is autosomal dominant,
every individual with the condition will have a
parent with the condition.
• Recessive: If the condition is recessive, an individual
with the condition can have one, two, or neither
parent exhibit the condition.
• Heterozygous/Homozygous: If individuals with
autosomal traits are homozygous dominiant or
heterozygous, their phenotype will show the
dominant allele. If individuals are homozygous
recessive, they will show the recessive allele.
Autosomal or Sex-Linked
• Autosomal: gene occurs on an autosome.
– If a trait is autosomal, it will appear in both sexes
equally.
• Sex-Linked: gene occurs on an X or Y chromosome.
– A female with a recessive trait will only show it if it
occurs on both of her X chromosomes.
– Thus, males are more likely to exhibit sex-linked
recessive traits.
Complex Control of Characters
• Patterns of heredity are complex. Most of the time,
characters display more complex patterns of heredity
than the simple dominant-recessive patterns discussed
so far.
• Characters can be influenced by several genes.
– It isn’t always as easy as Punnett squares make it seem!
– Polygenic inheritance: when several genes influence a
character.
• Determining the effect of any one of these genes can be difficult.
Due to crossing-over and independent assortment, many different
combinations appear in offspring.
• Familiar examples of polygenic traits include eye color, hair color,
skin color, height, and weight.
Intermediate
Characters
• In Mendel’s pea-plants, one
allele was dominant over
another. Sometimes,
however, there is an
intermediate between the
two parents.
• Incomplete Dominance: an
individual that displays a
phenotype that is
intermediate between two
parents.
– In snapdragons (on right), the flowers
in a cross between red and white
parents appear pink because neither
the red or white allele is completely
dominant over the other allele.
Genes with 3 or more Alleles
• Multiple Alleles:
Genes with three
or more alleles.
• Example: ABO
Blood Groups are
determined by
three alleles:
– IA, IB, i
– IA and IBare both
dominant over I
– Combinations
of these three
alleles makes
four blood
groups.
Codominance
• Codominance: Both
traits are displayed at
the same times.
• Example: AB Blood
Group—A and B are
both dominant traits,
and if someone has
both alleles they have
an AB blood type.
Decoding the Information in DNA
• Gene: A segment of DNA in a chromosome that codes for a
particular protein.
• Traits such as eye color are determined by proteins built
according to instructions coded in genes in the DNA.
• Proteins are not built directly from DNA. RNA is also involved.
• RNA=Ribonucleic Acid
• Three Differences between DNA and RNA
– RNA is singled stranded rather than double stranded.
– RNA has ribose sugar rather than deoxyribose sugar.
– RNA has Uracil (U) rather than Thymine (T) bases. U pairs
with A.
Buck 2011
Decoding the Information in DNA
• A gene’s instructions for making a protein are coded in the
sequence of nucleotides in the gene. The instructions for making a
protein are transferred from a gene to RNA in a process called
transcription.
• Transcription: Making RNA using one strand of DNA as a template.
• Translation: in ribosomes, when mRNA (messenger RNA)
molecules are used to specify the sequence of amino acids in
polypeptide chains (precursors of proteins)
Gene Expression: The
manifestation of the
genetic material of an
organism in the form of
specific traits.
Buck 2011
Transcription: Making RNA
Buck 2011
The Genetic Code: Three-Nucleotide
“Words”
• Different types of RNA are made during transcription,
depending on the gene being expressed.
• When a cell needs a particular protein, mRNA (messenger
RNA) is made.
• Messenger RNA (mRNA): a form of RNA that carries
the instructions for making a protein from a gene and
delivers it to the site of translation.
• The information from mRNA is translated from the language
of RNA (nucleotides) to the language of proteins (amino
acids).
• The RNA instructions are written as a series of threenucleotide sequences on the mRNA called codons.
• Each codon along the mRNA strand corresponds to an amino
acid or signifies a start of stop signal for translation.
RNA’s Roles in Translation
• Transfer RNA (tRNA) molecules and ribosomes help in the synthesis of
proteins.
• Transfer RNA (tRNA): single strands of RNA that can carry a specific amino
acid on one end, folds into a compact shape and has an anticodon.
– Anticodon: a three-nucelotide sequenceo n a tRNA that is complementary to
an mRNA codon.
• Ribosomal RNA (rRNA): RNA molecules that are part of the structure of
ribosomes.
Buck 2011
Protein Synthesis in Prokaryotes
• Operator: piece of gene
that controls RNA
polymerase’s access to
the genes.
• An operon is a group of
genes that code for
enzymes involved in the
same function…this is
the lac operon.
• Repressor: is a protein
that binds to an
operator and physically
blocks RNA polymerase
from binding and strops
transcription.
When lactose is present, the lactose binds to the repressor and changes the shape of the
repressor. The change in shape causes the repressor to fall off of the operator. Now the
bacterial cell can begin transcribing the genes that code for the lactose-metabolizing enzymes.
Buck 2011
Controlling the Onset of Transcription
• Eukaryotic cells have more DNA than prokaryotic cells
therefore there are more opportunities for regulating gene
expression.
• Transcription factors: help arrange RNA polymerase in the
correct position on the promoter
– Enhancer: can be bound by an activator away from the gene
Buck 2011
Intervening DNA in Eukaryotic Genes
• In eukaryotes, a gene is not an
unbroken stretch of nucleotides.
• Many genes are interrupted by
introns.
• Intron: long segments of nucleotide
that have no coding information.
• Exons: portions of a gene that are
translated.
• This adds options to evolution!
appropriately joined
Buck 2011
Karyotype
• Karyotype: number of
Chromosomes in a cell
• 22 pairs of autosomes, 1 pair of
sex chromosomes
• 44 autosomes total, 2 sex
chromosomes total
• XX=female
• XY=male
• Can be used to identify gender and
chromosomal disorders.
• Incorrect chromosome numbers
are caused by nondisjunction of
chromosomes in meiosis—
meaning that the chromosomes
do not separate correctly.
Chromosome Disorders
• Sex Chromosome Disorders:
– Klinefelter’s syndrome (XXY)
– Triple X Syndrome (XXX)
– Turner’s Syndrome (XO)
– Jacob’s Syndrome (XYY)
• Autosomal Disorders:
– Down Syndrome (Trisomy 21)
– Monosomy 21
– Patau’s Syndrome (Trisomy 13)
– Edward’s Syndrome (Trisomy 18)
– Cri du Chat (partial deletion of chromosome 5)
The Evolution of
Prokaryotes
http://www.dkimages.com/discover/Home/Plants/FungiMonera-Protista/Cyanobacteria/Cyanobacteria-2.html
Scientists use fossils to study
evidence of early life on Earth.
Fossil: the preserved or mineralized
remains or imprints of an organism
that lived long ago.
The oldest fossils are 3.5 billion year
old prokaryotes.
Some of the first prokaryotes were
marine cyanobacteria.
Cyanobacteria: photosynthetic
prokaryotes
Helped release oxygen gas into oceans,
and eventually the air.
http://www.mbari.org/staff/conn/botany/phytopla
nkton/phytoplankton_cyanobacteria.htm
Buck 2011
The origins of Mitochondria and
Chloroplasts
Most biologists think that mitochondria and
chloroplasts originated as described by the theory of
endosymbiosis.
Theory of Endosymbiosis: mitochondria are the descendants
of symbiotic, aerobic eubacteria and chloroplasts are the
descendants of symbiotic, photosynthetic eubacteria
Bacteria entered larger cells, and began to live inside the cell
performing either cellular respiration or photosynthesis.
Buck 2011
Other Organelles
The folding in the plasma membrane may have been
the forerunner of both the endoplasmic reticulum and
nuclear envelope based on similar structure and
biochemical analysis.
Part of cell specialization: a process where cells
become modified to perform specific functions in an
organism.
http://picsbox.biz/key/rough%20endoplasmic%20reticulum%20function
http://en.wikibooks.org/wiki/Structural_Biochemistry/Cell_Organelles/Endoplasmic_Reticulum#Smooth_Endoplasmic_Reticulum_.28SER.29
Buck 2011
A singled
celled protist
Multicellularity
• Protists were the first eukaryotes. Protists
make up a large varied group of both
multicellular and unicellular organisms.
• Unicellular organisms are very successful,
but each cell must carry out all the
activities of the organism.
• Distinct types of cells in one body can have
specialized functions (like in your immune
system, for example).
• Almost every organism you can see
without a microscope is multicellular.
• Fossils of the first multicellular organisms
are about 700 million years old.
http://bio.rutgers.edu/~gb101/lab6_protists/m6a.html
http://sopastrike.com/strike
Multicellular
protists—
brownBuck
algae
2011
Mass Extinction and Continental Drift
The fossil record indicates that a  Continental drift also played an
sudden change occurred at the end important role in evolution.
of the Ordovican period—a large Continental Drift: the
percentage of organisms became
movement of Earth's land
extinct.
masses over Earth’s
Extinction: the death of all
surface through geologic
members of a species.
time. Resulted in presentMass Extinction: an episode
day position of the
during which large numbers of
continents.
species becomes extinct.
Helps to explain why there are
Mass extinctions can allow new
a large number of marsupials in
species to adapt and fill niches
both Australia and South
America, because these
previously occupied by the nowcontinents were once
extinct species, and thus help drive
connected.
evolution.
Buck 2011
The Ozone Layer
 While the sun gives us the light energy Earth’s organisms need, it also
produces dangerous ultraviolet (UV) radiation.
 Early life lived in the sea, which protected it from dangerous UV
radiation.
 However, land organisms needed protection.
 This protection is provided in the upper atmosphere by the ozone
layer which blocks UV radiation.
 The Ozone (O3—regular oxygen is O2layer formed about 2.5 billion
years ago as cyanobacteria began adding oxygen to the earth’s
atmosphere.
Buck 2011
Darwin’s Observations
 On his voyage, Darwin found evidence challenging the
belief that species do not change.
 Darwin read Charles Lyell’s book Principles of Geology
which proposed that the surface of Earth changed
slowly over many years.
 Darwin saw things that could be explained only by a
process of gradual change.
 In South America, he found fossils of extinct armadillos
which were similar but not identical to modern armadillos
in the area.
 Darwin visited the Galápagos Island and noticed that
the species on the islands were similar to those from
South America, but they changed since they arrived.
 Darwin called this Descent with modification, or evolution
Buck 2011
Evolution by Natural
Selection
 Darwin called this differential
rate of reproduction Natural
Selection.
 In time, the number of individuals
that carry inherited favorable
characteristics will increase, and
the population will change or
evolve!
 Organisms differ from place to
place because their habitats are
different, and each species has
reacted to its own environment.
 Adaptation: An inherited trait that
has become common in a
population because the trait
provides a selective advantage.
http://goose.ycp.edu/~kkleiner/ecology/EvolEcologyimages.htm
Buck 2011
Darwin’s Four Major Points
1. Inherited variation exists within the genes of every
population or species (the result of random mutation and
translation errors).

Or: Not every organism is identical!
2. In a particular environment, some individuals of a
population or species are better suited to survive (as a
result of variation) and have more offspring (natural
selection).

Or: Some organisms do better and have more babies!
3. Over time, the traits that make certain individuals of a
populations able to survive and reproduce tend to spread in
that population.

Or: Organisms that do better give their advantages to those
babies they had!
4. There is overwhelming evidence from fossils and many
other sources that living species evolved from organisms
that are extinct.
Buck 2011
Change Within Populations
• Darwin’s ideas were based on the idea that in any
population, individuals that are best suited to
survive will produce the most offspring. These traits
will become common new generations.
• Scientists now know that genes are responsible for
inherited traits. Certain forms of genes called
alleles become more common.
– In other words: natural selection causes the allele
frequency to change.
• Mutations and sexual reproduction provide the
variation needed for natural selection.
– Random gene mutation is essential to evolution!
Buck 2011
The Fossil Record
• Fossils offer the most
direct evidence that
evolution takes place—
fossils of animals show a
pattern of development
from ancestors to modern
descendants.
• Fossils provide a record of
Earth’s past life-forms.
• Evolution: Change over
time.
– Evolution can be observed
in the fossil record.
Buck 2011
Anatomy and Development
 Comparisons of anatomy of different types of organisms often
reveal basic similarities in body structures even though the
function may differ between organisms.
 Vestigial Structure: a structure in an organism that is reduced in
size and function and that may have been complete and
functional in the organism’s ancestors.
 Similarities in bone structure can be seen in vertebrates,
suggesting they have a relatively recent common ancestor


Homologous Structures: structures that share a common ancestry. Similar
structure in two organisms can be found in the common ancestor of the organisms.
Example: human arm, monkey arm
Analogous Structures: are features of different species that are similar in function
but not necessarily in structure and which do not derive from a common ancestral
feature (compare to homologous structures) and which evolved in response to a
similar environmental challenge. Example: bird wing, insect wing
 Evolutionary history of organisms is also seen in the
development of embryos. The stages of embryonic development
are similar in many species.
Buck 2011
Homologous Structures
Proteins and DNA Sequence
• Amino acid sequences of similar proteins were
compared.
• If evolution has taken place, then species descended
from a recent common ancestor should have fewer
amino acid differences in proteins than do species
that aren’t as closely related.
 This pattern does not hold true for all proteins. A
certain protein may evolve more rapidly in some
groups than others.
 Comparisons of proteins may not reflect
evolutionary relationships supported by the fossil
record and other evidence.
 More accurate hypotheses about evolutionary
histories are based on large numbers of gene
sequences.
 These evolutionary histories based on DNA
sequences tend to be similar to those from the
fossil record.
Buck 2011
Examples of Natural
Selection
 Tuberculosis (TB) is caused by
the bacterial species M.
tuberculosis and kills more
adults than any other infectious
disease in the world.
 Two effective antibiotics
because available to fight this
bacteria.
 However, in the late 1980s, new
strains of Tuberculosis that are
resistant to the antibiotics
appeared.
 These resistant bacteria evolved
through natural selection.Buck 2011
Gene Pools
 Natural selection utilized the diversity in a species’ gene
pool.
 Gene Pool: The total number of genes of every individual in
an interbreeding population.
 Gene pools contain variations in genes, relative gene
frequencies, and allele frequencies. Genetic recombination can
influence the gene pool and variation.
 Variations: A modification in structure, form, or function.
 Relative Frequency: the average number of occurrences of a
particular event in a large number of repeated trials.
 Allele Frequency: the frequency of an allele compared to
other alleles of the same gene in a population.
 Natural selection makes the most successful alleles
(different copies of genes) most common in a population.
 In this way, natural selection changes the POPULATION, not
the INDIVIDUALS!
Buck 2011
Formation of New Species
 Species formation occurs in stages.
 A species molded by natural selection
has an improved “fit” to its
environment.
 Divergence: The accumulation of
differences between groups.
 Divergent (split apart) Evolution: The
process by which an interbreeding
population diverges (splits) into two or
more descendant species, resulting in
once similar or related species to
become more and more different.
 Convergent (come together) Evolution:
A kind of evolution wherein organisms
evolve parts that have similar
structures or functions in spite of their
evolutionary ancestors being very
dissimilar or unrelated.
 Speciation: The process by which new
species form.
Buck 2011
The body structure of these organisms
are examples of convergent evolution.
http://bio1152.nicerweb.com/Locked/media/ch40/fast_
swimmers.html
Resources and Population Size
• As a population grows,
limited resources eventually
become depleted and
population growth slows.
• The Logistic Model: A
population model in which
exponential growth is limited
by a density-dependent
factor.
– Density-Dependent factor:
limited resources that become
depleted when the population
is larger.
Exponential Growth Curve:
Also called a
j-curve
Logistic Growth Model:
Also called
an s-curve
Growth Patterns in Real Populations
• Exponential Growth Patterns are
best to describe faster growing
organisms such as:
– Many plants
– Insects
Exponential Growth Curve:
Also called a
j-curve
• Logistic Growth Model is best to
describe slower growing
organisms such as:
– Bears
– Elephants
– Humans
• Density-Independent Factors:
environmental conditions
– Weather
– Climate
Logistic Growth Model:
Also
Also
called
called
a
an
j-curve
s-curve
Rapidly and Slowly Growing Populations
• r-strategists: grow
exponentially when
environmental conditions
allow them to reproduce.
K-strategists: organisms that
grow slowly with small
population sizes and a
population density usually
– Results in temporarily large
near the carrying capacity (K)
populations.
of their environment.
• When environmental
Generally K-strategists:
conditions are good, the
population grows rapidly.
Have a long life
When conditions are poor, the
Mature slowly
population size drops quickly.
Have few young
• Generally r-strategists:
Provide extensive care for
– Have a short life span
young
– Reproduce early
– Many small offspring
– Offspring mature with little
parental care
Allele Frequencies
• Allele Frequency: the frequency of an allele compared
to other alleles of the same gene in a population.
– Biologists began to study how allele frequency changed in
populations and wondered if dominant alleles (usually more
common than recessive) would spontaneously replace
recessive alleles in populations.
• Hardy and Weinberg demonstrated that dominant
alleles do not automatically replace recessive alleles.
– They showed that the frequency of alleles in a population
does not change.
– Also, the ratio of heterozygous individuals to homozygous
individuals does not change unless the population is acted on
by something that favors a particular allele.
The Hardy-Weinberg Principle
• Hardy-Weinberg Principle: allele frequencies in a population do
not change unless evolutionary forces act on the population.
• Hardy-Weinberg Equation: p2+2pq+q2=1
• When no evolutionary forces are acting on a population, it is in:
– Genetic Equilibrium: A relative measure of reproductive success of an
organism in passing its genes to the next generation.
• There are five principal evolutionary forces that can cause
genotype ratios to change:
1.
2.
3.
4.
5.
Mutation
Gene Flow
Nonrandom Mating
Genetic Drift
Natural Selection
Five Principle Evolutionary Forces
(Cause Genetic Change in a Population)
• Mutation: source of variation and makes evolution possible.
• Gene Flow: the movement of alleles into or out of a
population. Occurs because new individuals (immigrants) add
alleles and Departing individuals (emigrants) take alleles
away.
• Nonrandom Mating: when individuals prefer to mate with
others that live nearby, or are of their own phenotype, or
based on certain traits.
• Genetic Drift: the random change in allele frequency in a
population.
• Natural Selection: Causes deviations from Hardy-Weinberg by
directly changing allele frequencies, since some alleles are
being selected for.