Chapter 8 Flashcards by Carson Gafford

two main features affecting allele frequency

Genetic Drift and Natural Selection

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random, nonadaptive evolution

Genetic Drift

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Happens through adaptation

Natural Selection

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all genes are subject to this

Genetic Drift

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all genes are not subject to this

Natural Selection

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largely developed by Sewall Wright in the 30’s and Motoo Kimura in the 60’s

Theory of Genetic Drift

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the difference between your sample and the real population

Sampling error

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more than likely the small population will go to 0

Genetic Drift

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small independent population that interbreeds with one another

Deme

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set of Demes

Metapopulation

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May start out the same say p=0.5
But random changes may push one way or another
One deme goes one way & another may go the other way
Thus originally identical demes may become different

Random Fluctuations

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In a finite population, allele frequencies fluctuate even without NS

Genetic Drift

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Some alleles fixed, others lost, homozygotes increase

Genetic Drift

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Separate populations diverge

Genetic Drift

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Easier to alter large or small population sizes?

small

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most populations will go to..

fixation

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even large populations diverge from same…

starting point

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leads to homozygosity

-random, it could be good or bad

Fluctuations and population size

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example of loss of Heterozygosity

New zealand snapper fishery

overexploited
drift taken over
fewer heterozygotes
but 3,000,000 individuals!!
few reproduce

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how many bread

effective population size ( 200 in new zealand fishery )

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will alter it - only large ones mate for example

Natural Selection

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may allow offspring to mate with parents

Overlapping generations

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small repeats in DNA

Microsatallites

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evolve rapidly, and selectively neutral

Microsatallites

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can track population

Microsatallites

formed from slippage-induced mutation

Microsatallites

sea levels down, islands connected

Glaciation

drift is stronger in small populations?

true

history of a particular gene

Gene trees

Looking backwards, the alleles come together (coalesce) to a single individual

Coalescence

Chance: small populations will become monomorphic

Coalescence

Not all individuals have as many offspring

Coalescence

time to coalescence

2N | -N is population size in generations

Cannibalistic bugs – only 1 survives when they meet When there are a lot, they run into each other a lot When few, it is less likely

Bugs in a Box ex of coalescence

will quickly coalesce to beneficial mutation

positive selection

no coalescence

balancing selection

neutral drift

arises and slowly replaces the ancestral allele by drift

Multiregional Hypothesis | Multiple origins from H. erectus-like ancestor

Coalescence and Human Origins

Out of Africa – single origin of anatomically modern humans

Coalescence and Human Origins

Equal variation within populations | Africa, Europe, and Asia would all be monophyletic

Mutiregional

Greater variation in Africa | African populations non-monophyletic, some closer to Europe+Asia

Out of Africa- supported - African lineages - sequential sister taxa to rest of world - African lineages with far -more genetic diversity - Little divergence in rest of humans

Used coalescence to find

mitochondrial Eve

Ancestor of all human mitochondria | Estimates are about 156,000-250,000 YA

- This ancestor existed prior to the divergence of modern populations - Values much more recent than if human populations descended separately from archaic Homo sapiens

Mitochondrial Eve

- Support out of Africa Hypothesis | - Variation and mutation rates leads to effective breeding population of 4,600-11,200 people

Mitochondrial Eve

- Must have been a fairly cohesive group in Africa | - Could not have been spread around because too few of them to form cohesive species if also in Europe and Asia

Mitochondrial Eve

-Brief period of small population size -Only some make it through Reduce variation

Population bottlenecks

No variation in 62 enzyme-coding loci Unusually high homozygosity for a natural population More than in Southern Elephant seal 30,000 individuals now But 20 in the 1890’s And even lower effective size because only 20% of males reproduce

example of population bottlenecks | -museum samples from before the bottleneck had greater variation

Change in allele frequencies as a result of the small number of individuals that colonize a region

Founder effect

Retreating glaciers created habitat | Spruce that colonized new habitat from... what?

leading edge

- nuclear DNA - mitochondrial DNA - Dispersed by wind, but not far

seeds

- nuclear DNA | - Long distance dispersal by wind

pollen

Gamache et al. did 1000k N-S transect

Leading Edge Founder Effect

Mitochondrial – 1 haplotype in N

Leading Edge Founder Effect

Nuclear same types as in S

Leading Edge Founder Effect

High between population variability throughout N for mitochondria

Leading Edge Founder Effect

Hallmark of drift

Leading Edge Founder Effect

Nuclear not variable between sites

Leading Edge Founder Effect

believed Slightly beneficial allele with fitness of 1+s arises in large population

Haldane

Fixation probability determined to be

population large, effects strong

selection dominates

selection week, population small

drift dominates

for initial mutation, population ________

drops out

s>1/2Ne

drift

s<1/2Ne

selection

PA with highest fitness

Overdominance

introduced a tremendous amount of variation

cross-breeding

drift only important in _____ generation

first

_____ not different in large vs. small treatments as a whole

variation was greater in the

small population

led to discovery of differences of amino acid sequence without phenotypic differences

electrophoresis

Too much variation to explain by NS

Neutral theory of molecular evolution

are neutral, not mutations

substitutions

generally are deleterious and are purged from the genome by NS

mutations

More closely related things had fewer differences

AA clock

all members of clade should be equally distant from outgroup

Genetic equidistance | -So a bird, a lizard, a human, and a frog should have the same number of differences from a fish

Multiple hits at same site – more likely with time - More likely at 3rd position - By applying what is known, we get a halfway decent clock

Saturation

Appears to not have an effect | Molecular clock and fossil divergence dates the same in mammals

Generation time