Download - Free Documents

Chapter Population Genetics
OBJECTIVES Relate the study of genetics to that of population genetics and discuss factors
that can affect genepool equilibrium Explain the HardyWeinberg model Discuss evolution
through natural selection Explain genetic drift and contrast its effects on large and small
populations. Discuss the role of quantitative traits in microevolution.
Population Genetics
Recall variation among individuals allows populations to adapt to new environmental
conditions or to be selectively bred for desirable traits.
Types of Evolution
Microevolution change within a species. Occurs over dozens or hundreds of generations
Macroevolution Much longer time period. Results in a new species
A More Precise Definition
Microevolution is a change in the genetic composition of populations.
Studied by population geneticists.
Gene pool
All alleles in a population of organisms.
Allele frequency
Percentage of a particular allele in one population. Ex In a population of pea plants that are
all homozygous for purple flowers, allele freq. for purple flowers is A change in an allele
frequency is an indication of evolutionary change.
Allele Frequencies within Beetle Population
Polymorphic Populations
Have or more alleles for a particular trait. Ex humans are polymorphic for blood type. Ex
apple trees are polymorphic for fruit color.
Hidden Genetic Variations
Mutation in noncoding regions of DNA Silent mutations code for the same amino acid
Unseen polymorphisms
The HardyWeinberg Model
An idealized mathematical model of gene pools. Mathematician Godfrey H. Hardy Physicist
Wilhelm Weinberg
Use allele freq. to calculate genotype freq.
Allele frequency p and q, p q In the next generation
p pq q
Homozygous p p Heterozygous pq Homozygous q q
HardyWeinberg Equilibrium
Allele and genotype frequency will stay constant in the absence of disturbing influences. p pq
q
HardyWeinberg Model
Makes some assumptions about the population. No disturbing influences. random mating no
mutation the alleles dont change no migration or emigration infinitely large population size no
selective pressure for or against any traits.
HardyWeinberg Equilibrium
Predictions of the model . Predicts allelic and genotypic frequencies . Genetic variation
remains in the population unless selective pressures Good news for Darwin Assumed
blending inheritance.
Genetic equilibrium a constant state of allele frequency
The following conditions must be met in order that genetic equilibrium not be disrupted. No
natural selection Random mating No migration No mutation Large population size
Note does not occur in nature. So, why use HardyWeinberg model
Quick Quiz
. Would a change in allele frequencies be more likely to produce microevolution or
macroevolution . What is the difference between gene pools and allele frequencies . Why
does the concept of gene pools apply to populations but not to species
A Normal Distribution results from Stabilizing Selection Natural selection that favors average
individuals in a population.
Normal Distribution
IQ
Females only mate with males with the largest tails. Over time, tails have gotten continually
larger due to this selective pressure.
Directional Selection in Peacocks
Peppered Moths color variations
allele frequency was light, dark allele frequency dark, light
Disruptive Selection Natural selection that favors either extreme trait.
Disruptive Selection in Snails
Limpets with lightcolored shells blend in with light rocks and sand. Dark shells blend in with
dark rocks. Limpets with mediumcolored shells are easily seen on both rocks and eaten by
birds.
Disruptive Selection in Spiders
When spiders are small, they are not as easily seen by predators. When spiders are large,
they are often too big to be eaten. Spiders in the middle are the most vulnerable to predators.
Other Factors Affecting Gene Pools
Gene Flow Migration to a new population, organism may bring new alleles with it. Mutation If
beneficial, will be favored by natural selection and gradually increase in frequency Genetic
Drift Spontaneous changes in allele frequencies. Small populations only.
Other Factors Affecting Gene Pools
Inbreeding Gradual increase of homozygotes. Ex California Condor Population bottleneck
Population size reduced for a few generations. Inbreeding results. Ex Buffalo in the s.
Inbreeding increases frequency of harmful recessive alleles. Leads to Inbreeding Depression
reduced fertility and survival.
Did you know
The average human is estimated to have alleles that would be lethal if they were
homozygous In inbred populations, inheriting of these alleles is more likely.
BSCS Biology A Molecular Approach
Population Genetics
CONCEPT REVIEW Evolution results from a disruption in genetic equilibrium. The normal
distribution of variations in a population can be changed by natural selection, gene flow,
mutations, and genetic drift
Chapter Diversity and Variation
Outcomes Explain homology and give examples of homologous structure Describe how the
general characteristics of the kingdoms differ.
The or Kingdoms
Archaebacteria Eubacteria Protista Fungi Plantae Animalia Bacteria/monera
Bacteria
Prokaryotes First organisms to evolve
Protista
Earliest eukaryotes. Usually single celled. No organ systems Nucleus developed
Mitochondria, flagellates, and plastids became incorporated. Ex amoeba, paramecium, algae
Fungi
Usually multicellular except yeast Eukaryotic Heterotrophs Evolved from funguslike protists
slime molds Ex mushroom, mold, yeast
Plantae
Multicellular, with complex body systems roots, stem, leaves Autotrophs Eukaryotes Evolved
from photosynthetic bacteria Ex Flowering plants, Conifer, Mosses, Ferns
Animalia
Multicellular with complex systems Heterotrophic Eukaryotic Ex Fish, Amphibian, Reptile,
Bird, Mammal
There are still lobefinned fish today called mudskippers. species have been identified. Unlike
those we evolved from, most of todays species have only appendages front lobefins
Fish to Amphibians
Reptiles to Birds
Reptiles to Birds
Evolution of Mammals
Eventually, some mammals returned to the water.
Todays whales had an ancestor similar to a wolf.
Chapter Changes in Species
Outcomes Cite evidence from fossils, ecology, and homologies that support the theory of
evolution Discuss the genetic and molecular evidence for evolution Discuss isolation
mechanisms that can cause speciation Describe the patterns in evolution such as
punctuated equilibrium
Fossils
as evidence of evolution
Fossils are the preserved remains or imprints of ancient organisms.
Fossils the only evidence we have that tells us directly about life in the past.
This extinct dragonfly had a wingspan of feet
Life first appeared on earth more than billion years ago.
Fossils of algae and diatoms
Millions of now extinct creatures lived on earth before humans came along.
Some fossils are the actual preserved remains of the organism
SoftTissue Fossils
Ice in the Arctic has preserved some fossils for ,s of years. In a wooly mammoth was
discovered intact. Can it be revived by crossing with an elephant Different s of chromosomes
and , but similar DNA.
Scientists have found , species of extinct orgnisms Estimate that only in , have been found.
Evolution of the Horse
In these pictures, there appears to be a straight line progression from the first horse ancetor
to the modern horse species. Such a progression implies an evolutionary goal, since there is
a trend toward larger body size and fewer toes.
Evolution of the Horse
However, evolution rarely follows a straight line to a goal. Remember, There are no goals in
evolution
Evidence for Evolution
Body Structures homologous vestigial analogous
Homologous Structures Traits that are
similar in different species because they share a common ancestor.
Note how the bones have adapted to different niches This is evidence of a common
ancestor.
Vestigal Structures No longer used.
The Human Tailbone This is evidence that humans evolved from an ancestor that had a tail.
Vestigal Organ human appendix
appendix
A whale has a pelvic bone too, and tiny leg bones.
Analogous Structures structures that
are similar in function but are not inherited from a common ancestor.
NOTE Analogous structures indicate that organisms are not related.
Embryology is also used as Evidence of Evolution Similar development of the embryo is
evidence of a common ancestor
All three embryos have gill pouches in the folds of the neck. All three have tails.
Perhaps the clearest biochemical evidence of the common origin of living things is the
genetic code. The same nitrogen bases of adenine, thymine, guanine, and cytosine exist in
every form of life.
In addition, the genetic code itself the codons for the amino acids is almost universal.
The genetic code is the same in every known organism. Every organism uses the same base
codes for amino acids
Degree of Relatedness Can be determined by
Amino acid sequence Homologous proteins Nucleotide sequence Homologous genes.
More Genetic Evidence Pseudogenes
Gene duplication produces multiple copies of DNA sequences. Pseudogenes gene copies
that dont function, so arent subject to natural selection. Mutations occur unchecked.
According to natural selection, these noncoding sections should accumulate mutations faster
than functional genes and they do
Amino Acid Sequence
Can be used to determine relatedness
How fast do evolutionary changes take place
Based upon Darwins theory it has long been believed that evolutionary changes were slow
and gradual Gradualism.
scientists Stephen Jay Gould and Niles Eldridge advanced a different explanation about the
rate of evolution called Punctuated Equilibrium
Punctuated Equilibrium populations remain genetically stable for long periods of time,
interrupted by brief periods of rapid change. sudden changes in the environment increased
mutation rate.
stasis
Speciation is the evolution of one or more species from a single common ancestor species.
Patterns of Evolution
How do species remain separate
Potential mates do not meet. Grizzly and Polar bears. Potential mates meet but do not
breed. Nocturnal and diurnal birds. Leopard frog populations that breed during different
months. Potential mates meet and breed, but do not produce viable offspring.
Divergent Evolution
Occurs when isolated populations of a species evolve independently.
Grizzly Bear
Polar Bear
Divergent evolution is responsible for polar bears. A northern population of grizzly bears
became isolated from others of the species and adapted to the Arctic regions.
Coevolution
Interactions with other organisms effect evolution. Coevolution is responsible for mimicry one
of the most fascinating topics in biological evolution.
Coevolution The pronuba moth and the yucca flower
Depend on one another for reproduction.
Coevolution The Orchid Fly
Coevolution Cactus and Galapagos Tortoise
Saddleback shell
Cleaner Wrasse
Sabre Toothed Blennie
Adaptive Radiation Many diversely related species from one common ancestor
Polyploidy in Plants
If plants inherit an extra chromosome from parents, they are said to be polyploidy. Often,
these plants can only mate with other polyploids, or use asexual reproduction.
Convergent Evolution
Unrelated species display similar features. No common ancestor. How does this happen
Convergent Evolution
Disruptive markings make it hard for predators to single out a victim.
Similar niches usually contain similar evolutionary pressures selective pressures. If ancient
niches were similar to modern niches then organisms today could resemble organisms now
long extinct.
Similar niches found on different continents can produce organisms that are fairly similar.
Modern dolphins and prehistoric ichthyeosaurs marine reptiles look very similar due to the
types of niche they inhabited.
Analogous structures can be caused by niches. Similar niches create similar body forms. .
.
.
..
Note how similar niches created long necks in both sauropods and giraffes.
.
.
.
Similar foods similar niches create similar teeth in herbivores.
.
Similar foods similar niches create similar teeth in carnivores.
Quick Quiz
. What are isolating mechanisms, how do they operate . What is polyploidy What is its
connection to speciation . Explain the statement Populations evolve, not individuals within a
population.
Origin of Species
Concept Review
New species can develop when populations become separated and isolated. Similar traits
can develop in unrelated species occupying comparable niches. Interactions with other
organisms affect evolution. Many diverse species can evolve from one ancestral species.
Chapter The Origin of Life
Objectives Describe the origin of the universe and probable conditions on early Earth
Evaluate hypotheses about the origin of life and identify the probable characteristics of early
lifeforms Distinguish between chemical and biological evolution Describe the fossil record for
prokaryotes and eukaryotes.
The Origin of Life
Cant be observed Inferences Probably needed energy, C, H, O, N, and lots of time.
The Big Bang The Expanding Universe
Edwin Hubble, . The Hubble Telescope was named for him. Wavelengths of light can be
measured, spread out as objects move farther away The rate of expansion is known, used to
calculate the time when universe was tiny.
The Big Bang
billion years ago Universe was condensed into a tiny singularity An infinitely hot, dense
mass. When it exploded, The Big Bang, hurled energy and mass into space. What was there
before the Big Bang
Early Earth
. Billion years ago Meteorites and the oldest rocks from the Moon confirm this
History of the Earth
Era Cenozoic Mesozoic Million Years Ago
First evidence of
Humanlike apes Primates Flowering Plants Mammals Dinosaurs Reptiles Amphibians Land
Animals Land Plants Vertebrates Eukaryotes Free O in atmosphere by prok. Prokaryotes
Paleozoic
Precambrian
The Early Atmosphere
Gasses from volcanoes N, CO, HO, H, CO, probably methane CH No O No ozone layer
intense radiation, extreme temperature changes.
The First Living Things
Anaerobic Organisms billion years later, some photosynthetic organisms began releasing
free oxygen.
. Life originated on some other planet, then traveled to Earth through space. . Life originated
by unknown means on Earth . Life evolved from nonliving substances through interaction
with their environment. of these cannot be tested, only one can be stated as a hypothesis.
Which one
How did those living things come to be possible explanations
Chemical Evolution
Life evolved from nonliving substances Small, inorganic molecules were heated via cosmic
radiation, volcanoes, radioactivity and lightning. Gasses in the atmosphere react, forming
organic compounds Compounds accumulate in oceans, forming a hot soup Life evolved by
chemical reactions and transformations in the organic soup
Chemical Evolution
The oceans became soup of organic compounds
The Heterotroph Hypothesis
The first living things were probably heterotrophs that fed on organic compounds in the
ocean. With no competition, autotrophs would not have an advantage over heterotrophs
. There had to be a supply of organic molecules, produced by nonbiological processes. .
Some processes had to assemble those small molecules into polymers such as nucleic acids
and proteins. . Other processes had to organize the polymers into a system that could
replicate itself
The Heterotroph Hypothesis or OparinHaldane hypothesis Requirements
Evidence for the Heterotroph Hypothesis
Stanley Millers experiment in . Early Earth conditions were simulated in an airtight apparatus.
Water vapor Lightning CH, NH, HO, H After circulating for a week, new compounds were
found in the water, including some amino acids.
More recent experiments have produced the bases of DNA and RNA too.
Other Sources of Organic Molecules
Meteorites from space amino acids have been discovered Volcanic vents release gases at
high temperatures Remember st requirement There had to be a supply of organic molecules,
produced by nonbiological processes.
The rest of the hypothesis
. Some processes had to assemble those small molecules into polymers such as nucleic
acids and proteins. Clay repeating crystalline structure that could attract then connect
monomers . Other processes had to organize the polymers into a system that could replicate
itself RNA Can form spontaneously. Can reproduce itself. Probably came before DNA
Biological Evolution
When did chemical evolution become biological evolution When organic molecules became
living things Self reproduction, mutation that can be inherited, and natural selection life Cells
Today all living things are made of cells. It is unknown when/how cell membranes developed.
The first living things may have had membranes, or not. They may have been DNA, RNA,
proteinswho knows
Prokaryotic Fossils
. Billion years old. Singlecelled prokaryotes. Suggest life was already diverse and thriving.
Probably methanogens Use CO to oxidize hydrogen
Fossils of Eukaryotes
. Billion years old Lynn Margulis of UMass, Amherst developed the endosymbiont
hypothesis Chloroplasts and mitochondria were once freeliving prokaryotes. Photosynthesis
and respiration of the small cells have benefited the host cells. Mitochondria probably
evolved from aerobic, heterotrophic purple bacteria. Plastids probably evolved from
autotrophic cyanobacteria.
Endosymbiont Hypothesis
The evidence Both have their own DNA and ribosomes, which are similar to other bacteria.
Also both have a double membrane their outer membranes may have evolved from vacuoles
when host cells took them in.
Evolution of Eukaryotes
Quick Quiz
. Why is it believed that methanogens might have been the first organisms . How might
mitochondria and plastids have originated . What evidence supports the idea that
mitochondria and plastids originated from freeliving prokaryotes
Outcomes Describe how modern humans differ from other primates Evaluate the techniques
used to study evolutionary relationships in humans Compare early hominids with Homo
erectus and Homo sapiens Give reasons for the difference in the gene pools of modern
human populations.
Chapter Human Evolution
What are Primates
Opposable Thumbs Fingers and toes have nails, not claws Flexible shoulder and hip joints
Binocular, D vision for accurate depth perception Color vision
Humans vs. Other Primates
Bipedal Hands are free Have a hippocampus brain region for memory and learning. Absent
in most primates not chimps and gorillas More fine motor control in hands Language, well
developed vocal chords
Molecular Similarities Human vs. Chimpanzee
Protein Hemoglobin Myoglobin Cytochrome C Serum Albumin Number of amino acids
Aminoacid difference
Molecular Similarities Among Primates
Species compared Difference in DNA sequence Chimpanzee vs. . Bonobo Human vs. .
Chimpanzee Human vs. . Gorilla Gorilla vs. . Chimpanzee Estimated time since divergence
million years million years million years million years
Early Hominids
Lived in Africa Genera in Hominid family Homo and Australopithecus larger teeth, smaller
brains.
The Hominids
Hominids The Humanlike Primates
Comparing Skeletons
Skeletal fossils clues to how organism moves, eats, behaves. Footprint fossils How organism
moved, how heavy it was. Who was Lucy
Comparing Skeletons
Skeletal fossils clues to how organism moves, eats, behaves. Footprint fossils How organism
moved, how heavy it was. Who was Lucy
Australopithecus afarensis found in Ethiopia,
The First Humans
Hominids
Hence, both in space and time, we seem to be brought somewhat near to that great fact that
mystery of mysteries the first appearance of new beings on this earth.
Charles Darwin