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Transcript of Notes Evolution May
Chapter 16Population Genetics
OBJECTIVES: • Relate the study of genetics to that of
population genetics and discuss factors that can affect gene-pool equilibrium
• Explain the Hardy-Weinberg 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.
2 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 poolAll 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 100%
A change in an allele frequency is an indication of evolutionary
change.
Allele Frequencies within Beetle Population
Polymorphic Populations
• Have 2 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 non-coding regions of DNA
• Silent mutations code for the same amino acid
• Unseen polymorphisms
The Hardy-Weinberg ModelAn 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 = 1
In the next generation:
p2 + 2pq + q2 = 1
Homozygous p: p2
Heterozygous: 2pq
Homozygous q: q2
Hardy-Weinberg Equilibrium
Allele and genotype frequency will stay constant in the absence of
disturbing influences.
p2 + 2pq + q2 = 1
Hardy-Weinberg Model
Makes some assumptions about the population. No “disturbing influences.”
• random mating • no mutation (the alleles don't change) • no migration or emigration • infinitely large population size• no selective pressure for or against
any traits.
Hardy-Weinberg Equilibrium
Predictions of the model1. Predicts allelic and genotypic
frequencies 2. Genetic variation remains in the
population (unless selective pressures)
Good news for Darwin! (Assumed blending inheritance.)
Genetic equilibrium: a constant state of allele
frequencyThe following conditions must be met in order that genetic equilibrium not be
disrupted.1)No natural selection
2)Random mating
3)No migration
4)No mutation
5)Large population sizeNote: does not occur in nature.
So, why use Hardy-Weinberg model?
Quick Quiz
1. Would a change in allele frequencies be more likely to produce microevolution or macroevolution?
2. What is the difference between gene pools and allele frequencies?
3. 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
Directional Selection in Peacocks
Females only mate with males with the largest tails. Over time, tails have gotten continually larger due to this selective pressure.
Peppered Moths: color variations
1850: allele frequency was 95% light, 5%
dark
1900: allele frequency 95% dark, 5% light
Disruptive Selection: Natural
selection that favors either extreme trait.
Disruptive Selection in Snails
Limpets with light-colored shells blend in with light rocks and sand. Dark shells blend in with dark rocks.
Limpets with medium-colored 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 1800’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 7 alleles that would be lethal if they were homozygous? In inbred populations, inheriting 2 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 18Diversity and Variation
Outcomes• Explain homology and give examples
of homologous structure• Describe how the general
characteristics of the 5 kingdoms differ.
The 5 (or 6) 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 fungus-like 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 lobe-finned fish today called mudskippers. 34 species have
been identified. Unlike those we evolved from, most of today’s species have only 2 appendages (front lobe-
fins)
Fish to Amphibians
Reptiles to Birds
Reptiles to Birds
Evolution
of
Mammals
Eventually, some mammals returned to the
water.
• Today’s whales had an ancestor similar to a wolf.
Chapter 19Changes 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 3 feet!
Life first appeared on earth more than 3 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
Soft-Tissue Fossils
Ice in the Arctic has preserved some fossils for 1,000s of years.
In 1999 a wooly mammoth was discovered intact.
Can it be revived by crossing with an elephant? Different #s of chromosomes (58 and 56), but 95% similar DNA.
Scientists have found 250,000 species of extinct orgnisms
Estimate that only 1 in 10,000 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 !
1) homologous2) vestigial 3) analogous
Evidence for Evolution:
Body Structures
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.
appendix
Vestigal Organ: human 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 RelatednessCan 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 don’t function, so aren’t subject to natural selection.
Mutations occur unchecked. According to natural selection, these non-
coding 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 Darwin’s theory it has long been
believed that evolutionary changes were slow and gradual: Gradualism.
1972: 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?
(1) Potential mates do not meet. Grizzly and Polar bears.
(2) Potential mates meet but do not breed. Nocturnal and diurnal birds. Leopard frog populations that breed during different months.
(3) Potential mates meet and breed, but do not produce viable offspring.
Divergent Evolution:
Occurs when isolated populations of a species evolve independently.
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.
Grizzly Bear Polar Bear
Coevolution:
Interactions with other organisms effect
evolution.
Coevolution is responsible for mimicry
one of the most fascinating topics in biological evolution.
CoevolutionThe pronuba moth and the
yucca flower
Depend on one another for
reproduction.
CoevolutionThe 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 PlantsIf 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
1. What are isolating mechanisms, how do they operate?
2. What is polyploidy? What is its connection to speciation?
3. 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 17The 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 life-forms
• Distinguish between chemical and biological evolution
• Describe the fossil record for prokaryotes and eukaryotes.
The Origin of Life
•Can’t be observed
•Inferences
•Probably needed energy, C, H, O, N, and lots of time.
The Big BangThe Expanding Universe
• Edwin Hubble, 1920. 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
• 15 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
• 4.6 Billion years ago• Meteorites and the oldest rocks
from the Moon confirm this
History of the EarthEra Million Years Ago First evidence of
Cenozoic 7-565
Human-like apesPrimates
Mesozoic 140220235
Flowering PlantsMammalsDinosaurs
Paleozoic 300360400430520
ReptilesAmphibiansLand AnimalsLand PlantsVertebrates
Precambrian 210025003500
EukaryotesFree O2 in atmosphere by prok.Prokaryotes
The Early Atmosphere
• Gasses from volcanoes: N2, CO2, H2O, H2, CO, probably methane (CH4)
• No O2
• No ozone layer – intense radiation, extreme temperature changes.
The First Living Things
• Anaerobic Organisms• 1 billion years later, some
photosynthetic organisms began releasing free oxygen.
How did those living things come to be?
3 possible explanations:1. Life originated on some other planet,
then traveled to Earth through space.2. Life originated by unknown means on
Earth3. Life evolved from nonliving
substances through interaction with their environment.
2 of these cannot be tested, only one can be stated as a hypothesis. Which one?
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 EvolutionThe 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
The Heterotroph Hypothesis(or Oparin-Haldane
hypothesis)3 Requirements1. There had to be a supply of
organic molecules, produced by nonbiological processes.
2. Some processes had to assemble those small molecules into polymers such as nucleic acids and proteins.
3. Other processes had to organize the polymers into a system that could replicate itself
Evidence for the Heterotroph Hypothesis
Stanley Miller’s experiment in 1950. Early Earth conditions were simulated in an airtight apparatus.
• Water vapor• Lightning• CH4, NH3, H2O, H2After circulating for a week, new
compounds were found in the water, including some amino acids.
More recent experiments have produced the 5 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 1st requirement: There had to be a supply of organic molecules, produced by nonbiological processes.
The rest of the hypothesis:
#2. 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
#3. 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, proteins…who knows?
Prokaryotic Fossils
3.5 Billion years old. Single-celled prokaryotes.
Suggest life was already diverse and thriving.
Probably methanogens:Use CO2 to oxidize hydrogen
Fossils of Eukaryotes• 2.1 Billion years old• Lynn Margulis of UMass, Amherst
developed the endosymbiont hypothesis: Chloroplasts and mitochondria were once free-living 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
1. Why is it believed that methanogens might have been the first organisms?
2. How might mitochondria and plastids have originated?
3. What evidence supports the idea that mitochondria and plastids originated from free-living prokaryotes?
Chapter 20Human Evolution
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.
What are Primates?
• Opposable Thumbs• Fingers and toes have nails, not
claws• Flexible shoulder and hip joints• Binocular, 3-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 SimilaritiesHuman vs. Chimpanzee
Protein Number of amino acids
Amino-acid difference
Hemoglobin 579 1
Myoglobin 153 1
Cytochrome C 104 0
Serum Albumin 580 7
Molecular Similarities Among Primates
Species compared
Difference in DNA sequence (%)
Estimated time since divergence
Chimpanzee vs. Bonobo
0.7 3 million years
Human vs. Chimpanzee
1.6 7 million years
Human vs. Gorilla
2.3 10 million years
Gorilla vs. Chimpanzee
2.3 10 million years
Early Hominids
• Lived in Africa• Genera in Hominid family: Homo
and Australopithecus (larger teeth, smaller brains).
The Hominids
Hominids – The Human-like Primates
Comparing SkeletonsSkeletal fossils – clues to how
organism moves, eats, behaves.Footprint fossils – How organism
moved, how heavy it was.Who was Lucy?
Comparing SkeletonsSkeletal 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, 1974
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