Evolution Exam 3

effective population size

number of individuals in an idealized population that would result in the genetic behavior observed

neutral theory

most change in DNA sequence due to neutral mutations rising to fixation by genetic drift NOT beneficial mutations rising to fixation by natural selection

natural selection eliminates

bad mutations

because so few mutations are available for natural selection to fix

most differences are due to genetic drift

synonymous mutation

amino acid unchanged

nonsynonymous mutation

changes amino acid

most neutral mutations pushed to high frequency via

genetic drift (chance)

negative or purifying selection

the elimination of bad mutations

positive selection

increases the frequency of good mutations

nonsynonymous mutations are likely to affect

fitness

E. coli, yeast, fruit fly

different codons are more likely to make same protein for each

How does codon bias relate to a synonymous and nonsynonymous graph

synonymous mutation moves to slower (deleterious) codon for same amino acid which broadens scope of available fixations

codon bias

unequal usage of synonymous codons within an organism's genome

selective sweep or genetic hitchhiking

strong positive selection for a particular mutation increases the frequency of closely linked mutations

with selective sweep/genetic hitchhiking

recombination is unlikely to separate other alleles on chromosome

fixed allele carries

close alleles along with it

background selection

selection against deleterious mutations reduces genetic variation at linked neutral sites

background selection gives opportunity to

act on silent mutations that are close to beneficial ones

haplotype

multilocus genotype of a chromosome

can calculate both …

allele frequency and chromosome frequency

same allele frequencies can have different

haplotypes

linkage equilibrium

genotype of a chromosome at one locus is independent of its genotype at another locus

linkage disequilibrium

nonrandom association between a chromosome’s genotype at one locus and its genotype at another

linkage disequilibrium equation

D=gABgab-gAbgaB

if D=0 then

linkage equilibrium

if product of D equation is different from allele frequency then

linkage disequilibrium

what mechanisms create linkage disequilibrium

selection on multilocus genotypes, mutation, and population admixture

selection events can eliminate

entire haplotypes

if any haplotype doesn’t exist automatically in

linkage disequilibrium

population admixture

when 2 populations fuse or mix

population admixture causes some haplotypes to be

underrepresented and some to be overrepresented

genetic recombination

creation of new combinations of alleles during sexual reproduction

selfing increases

homozygosity

2 starting populations in linkage disequilibrium (nonzero)

over 50 generations moves closer to linkage equilibrium

inversions tend to stay … because …

unaltered, recombination can’t act on them

most pairs of loci tend to be in linkage

equilibrium

plant selfing

linkage disequilibrium decays quickly

parthenogenesis

development of a new individual from an unfertilized egg

offspring of … have … than …

sexual reproduction, higher survivability, asexual reproduction

sexual reproduction restores

linkage equilibrium

hermaphrodites

selfing only

hermaphrodites and males

selfing and outcrossing

other hermaphrodites and males

outcrossing only

groups of hermaphrodites C. elegans experiment

50 generations in stressful environment and measured growth in normal environment. Outcrossing (sex) increased fitness.

genetic load

number of deleterious mutations (reduces fitness)

Mueller’s ratchet

clones in an asexual population can never obtain a genetic load less than that of the current low-load clone

mutational meltdown

deleterious mutations grow so high in an asexual population that it causes extinction

sexual reproduction creates a way to

remove deleterious mutations

red queen hypothesis

adaptation by one species causes reduction in fitness for antagonist species so each must continually adapt to maintain fitness

longflower tobacco

more loci=more variance; you can select in either direction to create original genotype

most traits are coded by

many loci

some individual loci have

strong affects

Quantitative Trait Loci (QTL)

portions of the genome that influence quantitative traits

Monkeyflower Experiment

Lewisii-bee pollinated and Cardinalis-hummingbird pollinated sister species. common ancestor was bee pollinated. crossed hybrids. most traits controlled by multiple loci but some loci can have strong effects.

Monkeyflower follow-up study

allele substitution at single loci produces pollinator shift

heritability=

Vg/Vp

Vp=

Vg+Ve

song sparrows

randomized eggs across nests to find that beak depth was highly heritable

what predicts response to selection

strength of selection and heritability

additive genetic variation

fraction of total genetic variation due to additive effects of genes (adding up individual effect of alleles)

dominance genetic variation

fraction of total genetic variation due to gene interactions like dominance

Vg=

Va+Vd

narrow-sense heritability (h²)=

Va/Vp

Broad-sense heritability=

Vg/Vp

heritability

phenotypic variation due to additive effects

melospiza melodia experiment:

some individuals are more successful at surviving and reproducing

selection differential

difference between mean phenotype of the selected individuals and the mean phenotype for trait of interest across entire population

Selection differential

mean of selected group-mean of entire population

response to selection=

s+h²

Selection gradient=

S/trait variance

breeder’s equation

R=h²s r=response to selection h=narrow-sense heritability s=selection differential

alpine skypilot experiment

tundra populations pollinated by bees and have 12% larger flowers. tested how many generations to go from normal to 12% larger. few individuals with small flowers had high fitness.

directional selection

extreme phenotype is favored over other phenotypes; reduces phenotypic variation

stabilizing selection

favors average phenotypes rather than extreme variations; reduces phenotypic variation

disruptive selection

favors both extreme phenotypes over average ones; increases phenotypic variation

nectar guides experiment

pollinators prefer nectar guides

oxpecker experiment

aren’t mutualistic with large mammals. do not eat ticks, pick at wounds, and eat wax

problem with oxpecker experiment

used domesticated cattle

zonostema vittigera experiment

dark wing bands and wing waving similar to jumping spiders. proved that they mimic jumping spiders to deter them.

why did outcrossing in the coevolution line increase over time in the C. elegans experiment

to keep up

why did outcrossing decrease over time in the evolution line in the C. elegans experiment

good alleles have been reached through sex so more beneficial to self to maintain genes