NEW NOTES ON CHAPTER 23
I.
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MODERN MICROEVOLUTION
Microevolution – the change in the frequency of alleles in the population. This is evolution
on its smallest scale.
Genetic variation can be produced by
o Mutations (chromosomal or point)
o Sexual reproduction (crossing over, independent assortment, random fertilization)
The opposite of microevolution is macroevolution (examines major changes in structures
over several different species and a long period of time – millions of years.)
Examples: NYTimes article on butterfly coloration and Mullerian mimicry Vs. Shabin’s research on animal
body structure and its genetic background.
II.
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THE HARDY-WEINBERG PRINCIPLE
This principle is used to test whether a population is evolving (the allele frequencies in the
population remain constant over generations, unless they are acted upon by other forces)
Key terms to know:
o Population genetics (studying the changes of genetic makeup of populations)
o Population (organisms that belong to the same species and live in the same area)
o Gene pool (sum of all genes and their types in a population)
o Fixed allele (only one version of a certain gene is available in the entire population)
– these alleles make the population less diverse – consequences?
o Allele frequency (% or decimal expression of a certain allele compared to other
alleles of the same gene in the population)
So when do we say that a population is not evolving?
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Populations are considered to be stable and not evolving if:
o No mutations
o No natural selection
o Random mating (no sexual selection)
o Very large populations that are not affected by genetic drift
o No gene flow
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These conditions can almost never be met, so allele frequencies change over generations.
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Populations are constantly evolving
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The level of change of allele frequencies (the rate of evolution) can be calculated by the HardyWeinberg equation:
p+q = 1 and p2 + 2pq + q2 = 1
Practice problems and PKU case study on HW principle.
III.
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MAJOR FACTORS THAT ALTER ALLELE FREQUENCIES (We learned these previous and do not
spend more time on it in class – see me with questions)
Natural selection
Genetic drift
Gene flow
IV.
VARIATIONS OF NATURAL SELECTION
 Relative fitness – the contribution of an organism to the gene pool of the next generation
relative to the contributions of other members.
Which person is more fit Octamom or Bill Gates? Why?
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Natural selection directly acts on the phenotype and indirectly influences the genotypes in a
population. It can alter the frequently distribution of heritable traits in three ways:
o Directional selection – one extreme is favored, shifting the frequency curve to that
direction. Example: black bears average body mass increased during periods of extreme
cold during glacial periods because they were more able to insulate their bodies and had
a smaller body surface to lose heat.
o
Disruptive selection – both extremes are favored while the middle range of a trait is
disadvantageous. Example: Beak size in finches became either large or very small
depending on the types of nuts they eat, while the middle beak size was less useful for
either type of nuts. OR In desert mice, the light colored individuals blend in more on
sand, the darker colored ones blend in more on volcanic rock, while the middle
coloration is disadvantageous on both locations.
o
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Stabilizing selection – acts against both extremes of phenotypes and favors the average.
Example: human birthweight.
V.
HOW IS GENETIC VARIATION PRESERVED IN A POPULATION:
 Diploidy – recessive alleles can remain hidden in a family for generations because the dominant
alleles overpower them in the phenotype
 Heterozygote advantage – In certain environments heterozygous individuals can have an
advantage to both homozygous dominant and homozygous recessive individuals.
Example: sickle-cell disease on tropical areas:
http://www.youtube.com/watch?v=1fN7rOwDyMQ
Frequency dependent selection – the fitness of a phenotype depends on its frequency in the
population. (Having the most common phenotype can be both advantageous or disadvantageous)
CHAPTER 24 – THE ORIGIN OF SPECIES
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I.
WHAT IS BIOLOGICAL SPECIES AND SPECIATION:
Speciation -- the evolutionary process by which new species arise. This is the intermediate level
between microevolution and macroevolution.
Biological species – groups of populations whose members have the potential to interbreed and
produce viable and fertile offspring.
II.
REPRODUCTIVE ISOLATION
Various biological barriers exist that prevent organisms of different species from reproducing with
each other and forming viable and fertile offspring.
Go over the concept map for the types of reproductive isolation. Examples are important
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III.
SPECIATION CAN TAKE PLACE WITH OR WITHOUT GEOLOGIC SEPARATION
Allopatric speciation – two populations become different because they are separated
geographically from each other. Examples of geologic events that can result in new species
formation are mountain range formation, separation of one lake into separate smaller lakes, land
bridge formation between lakes or segments of rivers etc. Example of species formed by allopatric
speciation – Darwin’s finches, Harris’s squirrel and white-tailed antelope squirrel on the opposite
sides of the Grand Canyon.
Sympatric speciation – species formation that does not require geologic isolation. A small part of a
population becomes a new population by one of a few mechanisms:
o Autopolyploid plants – during meiosis, nondisjunction occurs and plants chromosome
numbers double from 2n to 4n. These new plants cannot bread with the original diploid
members of the species. Ex. Farmed corn and wild maze.
o Polyploid separation – can sometime occur in animals
Adaptive radiation -- combines the previous two speciations. Occurs when many new species arise
from a single common ancestor. Typically occurs, when a few organisms make their way to new,
distant areas or when environmental changes cause numerous extinctions, opening up new living
space for organisms. Examples: Darwin’s finches, mammalian adaptive radiation after the
dinosaurs’ extinction, dinosaur adaptive radiation in the Jurassic period about 165 million years ago.
IV.
THE TEMPO OF SPECIATION
Gradualism – species descended from a common ancestor and gradually diverge more and more in
morphology as they acquire unique adaptations.
Punctuated equilibrium – a new species changes most as it buds from the parent species and then
changes little for the rest of its existence.
CHAPTER 25 – PHYLOGENY AND THE TREE OF LIFE
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I.
CAROLUS LINNAEUS – This should be known from last year
The father of taxonomy, came up with the binomial nomenclature system and the levels of
classification for living organisms
Binomial nomenclature: double Latin name is given to all living organisms (First is
capitalized and represents the genus name, second is lower case and represents the species
name)
Taxonomic categories: domain, kingdom, phylum, class, order, family, genus, species
(Mnemonics)
Checking of understanding:
1. Which category includes the most organisms?
2. Which category includes the less diverse group?
3. Which Latin name pair represents closer relatives:
o Canis lupus and canis familiaris
o Patella vulgata and Flox vulgata
II.
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IMPORTANT KEY TERMS RELATING TO CLASSIFICATION
Phylogeny – the evolutionary history of a species or group of species
Systematics – an analytical approach to understanding the diversity and relationships of
organisms both present-day and extinct.
Molecular systematics – a new branch of systematics that uses comparisons of DNA, RNA
and other molecules to infer evolutionary relationships between individual genes and even
between entire genomes.
Taxonomy – an ordered division of organisms into categories based on a set of
characteristics used to assess similarities and differences
Phylogenetic trees – systematic uses these branching trees to summarize hypotheses about
evolutionary relationships usually based on multiple sources and generally also show the time when
the species branched off from the common ancestors.
Case study
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III.
SOURCES OF EVIDENCE USED TO CREATE PHYLOGENETIC TREES
Comparative anatomy:
o Homologous structures – structures that have common origins but may look different
because they adapted to different environments (could be signs of adaptive radiation)
o Analogous structures – structures that have similar functions but come from different
ancestry – may be sign of convergent evolution (two organisms evolutionary process that
make them similar because they adapted to the same environment)
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Molecular systematics (or comparative biochemistry) – Comparing DNA, RNA and protein evidence
to establish evolutionary relationships. The more alike two organisms DNA are the more closely
related these organisms are. Some parts of the DNA molecule may change fast and can be used to
compare very closely related species (mtDNA) while other parts may change very slowly so can be
used to compare more distant species (DNA that is responsible for hemoglobin formation). DNA
data can be used to establish molecular clocks – used to measure absolute time by measuring the
rate of mutations.
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Cladograms – diagrams that are constructed to summarize shared characteristics among various
taxa.
IV.
DOMAINS OF LIFE
Group activity
V.
KINGDOMS OF LIFE
Group activity
CHAPTER 26 – THE HISTORY OF LIFE ON EARTH
I.
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II.
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THE EARLY HISTORY OF THE EARTH AND LIFE
The Earth formed about 4.6 billion years ago.
(http://ngm.nationalgeographic.com/2006/12/early-earth/video-interactive and
http://www.youtube.com/watch?v=QDqskltCixA )
During the early days the earth
was bombarded with meteorites and had very heavy volcanic activities. Than the ancient
atmosphere formed from methane, CO2, ammonia and nitrogen oxides, hydrogen and
hydrogen sulfide. The Earth was very hot.
The first life forms appeared around 3.5 billion years ago. These were single celled,
prokaryotic organisms that could live in the ancient anaerobic environment.
There are various theories that help to explain how life originally formed:
o Oparin – Haldane theory – earth’s early atmosphere had been a reducing
environment that helped the formation of organic molecules. The energy required
for the formation of organic molecules came from the UV rays of the sun that was
really strong at that time (no ozone).
o Miller – Urey – tested Oparin’s hypothesis in the lab and found that simple organic
molecules could be produced under ancient atmospheric conditions.
(http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter26/animation_-_millerurey_experiment.html )
o Early organic molecules could also have been produced during volcanic activities or
could have come from extraterrestrial sources. These were sources of even wider
variety of organic molecules.
o Macromolecules could have been produced on hot clay or sand surfaces in the lack
of enzymes.
o Protobionts – aggregates of abiotically produced molecules that are surrounded by
a membrane-like structure. Protobionts were able to reproduce, maintain an
internal environment and were able to perform metabolism. They could form
spontaneously during laboratory experiments.
o RNA world – The first enzymes ( ribozymes) and self-replicating molecules were
RNA molecules. The function of ribosomes and some ribosomal viruses prove that.
THE FOSSIL RECORD
Fossil record – is the sequence in which fossils appear in the layers of sedimentary rock that
constitute the Earth’s surface. The oldest fossils settle in the deepest layers of the earth
while the newer fossils are higher up. Fossils may be remnants of dead organisms (hard
shells, bones etc.) or impressions they left behind. Sedimentary rock is the best source of
fossils, but amber, peat bogs, tar pits and some other sources are also important. The fossil
record is incomplete because it favors organisms that have been around for a long time,
were relatively abundant, and had hard shells or hard bony skeletons. Only about 1 % of
ever lived organisms have fossilized remains.
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Dating fossil can happen in different ways:
o Radiometric dating – based on the decay of radioactive isotopes (NOT CARBON) to
determine the age of the rocks or fossils. It is based on the rate of decay, or half-life
of the isotope.
o Relative dating – uses the order of rock strata to determine the relative age of
fossils.
http://www.pbs.org/wgbh/evolution/library/03/2/quicktime/l_032_02.html
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html
III.
KEY EVENTS OF LIFE'S HISTORY
 The earliest living organisms were prokaryotes. Prokaryotes were the only inhabitants of
the earth from 3.5 - 2.1 billion years ago (Stromatolites -- earliest fossils).
 Some early prokaryotes were oxygen releasing, photosynthetic bacteria, similar to today's
cyanobacteria. These organisms started to release oxygen into the atmosphere. This
oxygen made aerobic life and cellular respiration possible (2.7 - 2.2 billion years ago)
 Eukaryotes appeared about 2.1 billion years ago.
o Most likely hypothesis that explains the appearance of eukaryotes is the
endosymbiotic theory -- mitochondria and plastids were once independent,
prokaryotic cells. These cells got engulfed by other, somewhat larger cells and
became endosymbionts of these cells -- meaning that they remained undigested
inside of the host cells and formed a symbiotic relationship with them.
(http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter4/animation__endosymbiosis.html)
o Evidence of the endosymbiotic theory:
1. These organelles have enzymes and transport systems that are similar
to prokaryotes'
2. Both organelles replicate by binary fission
3. Both organelles have circular, naked DNA chromosomes
4. Both organelles have ribosomes
 Multicellular organisms evolved about 1.2 billion years ago, at least that is how old the oldest
multicellular fossils are.
 Colonization of land -- occured about 500 million years ago when the first plants, fungi and
animals began to appear. By this time ozone formed a preventive layer around the atmosphere
that protected living organisms from harmful UV rays.
IV.
HOW DID DOMINANT GROUPS OF LIVING ORGANISMS RISE AND FALL?
 Continental drift – is the movement of Earth’s continents on great plates that float on the hot,
underlying mantle. Where the plates collided, mountains are uplifted and volcanoes form.
These processes alter the habitat of organisms substantially and promotes allopatric speciation
on a grand scale. Continental drift can explain why some fresh water reptile fossils turned up in
Ghana (West Africa) and in Brazil and why Australia lacks indigent placental mammals while is
rich in marsupials.
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(http://www.youtube.com/watch?v=ryrXAGY1dmE&feature=related
http://www.youtube.com/watch?v=NYbTNFN3NBo&feature=related )
Mass extinctions – the loss of large number of species in a fairly short period of time. These
result from global environmental changes (ice ages, global warming trends, changes in light
intensity etc.) Mass extinctions can drastically alter entire communities and can make entire
lineages of organisms disappear.
However, these mass extinctions also resulted in the adaptive radiation of other species that
were not dominant before.
CHAPTER 32 – INTRODUCTION TO ANIMAL DIVERSITY
I.
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MAIN CHARACTERISTICS OF ANIMALS:
Animals are heterotrophic organisms that ingest their food in most cases before
digesting it with enzymes (exceptions apply, such as spiders)
Animals are eukaryotic, multicellular organisms that do not possess a cell wall. As a
result, structural proteins (collagen) support and connect their cells.
They have specialized muscle and nerve cells that in most animals form tissues.
Their dominant life stage is diploid and they mostly reproduce sexually with egg and
sperm cells.
The zygote typically goes through the following stages:
o Zygote
o Successive mitotic divisions -- cleavage
o Blastula -- cleavage eventually forms a hollow ball with small cells on the
outside. The inside is a fluid filled cavity called blastocoels.
o Gastrulation – formation of embryonic tissue layers (ectoderm, endoderm) and
an archenteron (cavity inside of the endoderm) – the entire organism at this
stage is called a gastrula
http://www.youtube.com/watch?v=UgT5rUQ9EmQ
In some animals the adults develop directly from an embryo that is already similar to
the adult. However, in many animals development occurs through a series of
metamorphosis processes (ex. Zygote, larva, pupa, adult)
Hox Genes: Animals have a unique set of genes that are responsible for the
morphological features of the animal. These genes are very similar in very different
animals and likely developed very early on during early animal evolution.
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_04.html
II.
THE BODY PLAN OF ANIMALS
A. Symmetry:
 Asymmetry – lack of any observable internal or external symmetry (ex. Sponges)
 Radial symmetry – these animals have a top and a bottom area but not front and
back or left and right sides. (ex. Sea anemone, sand dollar). These animals are
frequently sessile or floating in water.
 Bilateral symmetry – these animals have a distinct left-right and front-back and topbottom sides. Most of these animals also have their sensory organs concentrated
on the front to observe a new environment fast and respond quickly to it. They
usually have a larger brain as well for more centralized processing of information –
cephalization. (ex. Lobster, lady bug, lion etc.)
B. Embryonic Tissue Layers:
What are tissues?
 Sponges lack true tissues but in all other animals, the tissues start to form during
gastrulation. These germ layers form the various tissues and organs of the body.
Diploblastic animals have only two tissue layers (Cnidaria), while triploblastic
animals have three tissue layers (all higher animal Phyla).
o Ectoderm – the outer tissue layer – gives rise to the outer covering and the
central nervous system of the animal
o Endoderm – the innermost tissue layer, which lines the archenteron. Gives
rise to the lining of the digestive tract, lungs (in vertebrates) and liver.
o Mesoderm – the middle layer of triploblastic animals. It forms the muscles
and all other organs between the digestive tract and the outer covering.
C. Body Cavities:
Look at them on the human torso.
 Body cavities cushion and suspend organs in the body, can act as a hydrostatic
skeleton, enable internal organs to grow and move independently.
 Acoelomates -- flatworms (Plathyhelminthes) belong in this group. They do not
have body cavities between the alimentary canal and the outer wall of their bodies.
 Pseudocoelomates – are triploblastic animals with a cavity formed from the
mesoderm and endoderm. (ex. Roundworms)
 Coelomates – have a real body cavity that is usually filled with fluid, and it separates
the digestive tract from the outer body wall. This coelom only forms from tissue
which originates from the mesoderm. (ex. All animals higher than roundworms)
D. Protostome and Deuterostome Development:
 The two main groups of animals with bilateral symmetry and three tissue layers are
protostomes and deuterostomes. They have different characteristics from each
other in three aspects:
i. Cleavage – protostome development starts with a spiral cleavage and the
cells fate is decided very early on (determinate cleavage), while
deuterostome cleavage is radial and the cells remain stem cells longer.
They do not have determined functions until later in development
(indeterminate cleavage).
ii. Coelom formation – the body cavity forms in different ways in these two
groups. In protostomes the coelom forms from a solid mass of the
mesoderm that splits into two . In deuterostomes the archenteron folds in
and forms pockets that becomes the coelom.
iii. The fate of the blastopore – the opening of the blastula is also very
different. In protostomes the blastopore becomes the mouth and the anus
opens up opposite to the blastopore. In deuterostomes, the blastopore
becomes the anus, while the mouth forms on the opposite end of the
animal.