Exam 2:Evolutionary Mechanisms Flashcards

Question

What are the 4 strategies of solving HW problems?

Answer 1

1. If given genotypes (AA,Aa,aa) calculate p and q by adding up total number of A and a alleles 2. If given phenotypes, use recessive genotype "aa" to find q^2 and then q and p 3. Use p^2+2pq+q^2 to find genotype frequencies 4. If p and q are NOT constant from gen to gen, then population is evolving

Answer 2

when individual phenotypes (genotypes) have greater net fitness

Answer 3

YES, fitness may NOT change allele frequency over time

Answer 4

the difference between the average fitness of individuals bearing the allele and the average fitness of the population as a whole, when 1 allele consistently enhances fitness relative to other alleles A=[p*(w11-wbar)]+[q*(w12-wbar)] ``` p= probability of an A1 allele finding itself in a A1A1 homozygote q= probability of an A1 allele finding itself in an A1A2 heterozygote ```

Answer 5

overall survival rate is % of individuals born that survive to reproductive age. Often measure % that survive over period of time

Answer 6

for any given genotype or phenotype, the average # of offspring born per individual

Answer 7

is survival and/or reproductive rate of genotype (or phenotype) relative to maximum survival and/or reproductive rate of other genotypes in populatio

Answer 8

Consequences of natural selection depend on dominance of fitness, i.e. whether fit phenotype is due to dominant or recessive allele; usually use selection coefficient (s) For a dominant allele: faster/more pronounced when jumping to fixation For a recessive allele: less pronounced jump to fixation, recessivee alleles can "hide" @ lo frequency and not affected by selection, when p

Answer 9

measure of relative strength of selection acting against a genotype, compares 2 phenotypes and provides a measure of proportional amount that given phenotype is less fit - s=0 means genotype is NOT selected against - means that s=1 (lethal, selection against genotype is total and makes NO contributions to the next generation) * S usually used to measure strength of selection against genotypes containing dominant allele relative to homozygous recessive (but selection in favor of genotypes containing dominant allele can be accommodated by using NEGATIVE S)

Answer 10

when there is dominance, often use selection coefficient (s) the difference between mutant homozygotes fitness and wildtype fitness, when latter is set to 1

Answer 11

one allele consistently enhances fitness or makes it stay the same(never reduce), results in the favored allele to increase in frequency, causes rapid fixation in a population, deleterious mutations driven extinct and kept @ lo frequency, acts on single locus in diploid; REMOVES variations (like drift but quicker) but can be replenished by mutations, frequency of alleles in infinite populations depend on balance between mutation+selection

Answer 12

result in differences in average excess of alleles when: - genotypes differ in fitness - current allele frequency are not in equilibrium

Answer 13

1. Environment changes causes relative fitness to change, pre-existing mutants favored by selection 2. environment remains constant, new mutations arise that enhance fitness (REMEMBER MUTATION RATE IS ALWAYS CONSTANT)

Answer 14

Often when an allele is is dominant can have difference in starting+jumping to fixation (lot more steeper when compared to a recessive allele), recessive alleles can "hide" @ lo frequency, if p

Answer 15

recessive disease alleles @ lo frequeency in almost all populations, as recessive alleles hide and are not affected by selection, dominant disease alleles @ even lower frequency, frequencies governed by selection-mutation balance

Answer 16

either recessive or dominant, 1 allele is favored, maintain alleles in population even one that are deleterious in one of the homozygous conditions; usually beneficial mutations go to fixation (positive selection) and deeleterious mutations tend to bee kept @ lo freq (negative selection)

Answer 17

heterozygotes most fit, tends to maintain variation in population bc it keeps both alleles, when A1 is rare tends to increase in freq, when common tends to decrease in freq w11w22 (overdominance)

Answer 18

heterozygotes least fit, tends to disfavor whichever allele rarer and favor whichever allele is common; prevents evolution ofo potentially beneficial alleles generated by mutation w11>w12

Answer 19

- random fluctuation of allele variants in a populations - happens ALWAYS in finite populations - decreases genetic variation - rate of heterozygosity lost by genetic drift dictated by pop size (larger pop=longer time to get to fixation) - drift increases as pop gets smaller - acts on all LOCI compared to directional selection which only acts on 1 - jaggedness on graph

Answer 20

- higher selection=faster fixation - when no directional selection ONLY drift, population size determines the rate because small populations more EASILY lose variation faster (think about probability, more likely to get equal numbers of heads and tails in 100 rounds vs only 10) -important to remember that directional selection overcomes genetic drift in LARGE populations and when favored allele has high initial frequency

Answer 21

initial frequency is the chance of an allele to go to fixation ex: if the starting frequency of allele A is 0.5 then it has a 50% of going to fixation or a 50% chance of getting lost given that there is NO selection

Answer 22

- higher selection=faster fixation - when no directional selection ONLY drift, population size determines the rate because small populations more EASILY lose variation faster (think about probability, more likely to get equal numbers of heads and tails in 100 rounds vs only 10) -important to remember that directional selection overcomes genetic drift in LARGE populations and when favored allele has high initial frequency

Answer 23

heterozygotes most fit, tends toward equilibrium allele frequency, tends to keep allelic variation, w11w22; frequency of allele likely to gravitate toward a stable equilibrium freq ex:codominace and incomplete dominance

Answer 24

heterozygotes least fit, unstable equilibrium, favors whichever allele has a high frequency, rare alleles lost common alleles usually go to fixatio, w11>w12; one allele likely go to fixation other lost depennds on initial allele freq. ex:mimicry

Answer 25

Directional selection will overcome G.D. in large populations + when favored allele is already @ high frequency, ineffective in small populations (i.e. favored allele may not get fixed in smaller pops) Directional selection INEFFECTIVE for rare alleles in small pops

Answer 26

1. Directional: one extreme favored 2. Stabilizing: Average values are favored 3. Disruptive: both extremes are favored

Answer 27

NO!! Overdominant selection favors heterozygous GENOTYPES and tends to MAINTAIN allelic variation at ONE locus, while stabilizing selection favors PHENOTYPES near the mean and tends to REMOVE allelic variation @ MANY LOCI

Answer 28

favors phenotype near both extremes, increase variance/standard deviation of trait, tends to MAINTAIN allelic variation

Answer 29

favors phenotypes near the mean, tends to remove allelic variation @ many loci, variance decreases, powerful agent of conservation

Answer 30

one extreme favored, population mean moves, variance decreases, favored allele fixed

Answer 31

equilibrium of number of deleterious alleles created by a mutation in a population occurs at the same rate @ which deleterious alleles eliminated by selection

Answer 32

fitness of phenotype depends on how "common" it is in the pop positive= common phenotypes favored; fitness of phenotype/genotype increases as it becomes more common ex:pathogen-host coevolution negative=rare phenotypes favored, as allelic fitness decreases with increasing frequency in the protection of rare alleles ex: self-incompatability allele

Answer 33

u=d/2t t=divergence u= rate of allele substitution of generation

Answer 34

1. Impact of mutation on fitness, s 2. effectiveness of selection vs drift (chance) determined by population size Ne 3. So when Ne*s is very small (either Ne or s) then allele will have about same probability of fixation as neutral allele when 2Ne*s<1 an allele behaves as though it was neutral, neutral alleles have probability of fixation of 1/2N -expect to see higher mutation rates in smaller populations

Answer 35

- when no selection, depends on mutation rate | - when selection active, rate depends on rate of mutation + strength of selection + population size

Answer 36

- Selection occurs when Ne*s >1 - Drift occurs when Ne*s<1 - -if not too negative, could happen that mildly deleterious allele goes to fixation

Answer 37

sperm (haploid) sensitive to genetic load- build up of deleterious alleles, mutational meltdown

Answer 38

1. Bottleneck Effect - sudden reduction in pop size due to change in environment or fragmentation, new gene pool may not. reflect original, if pop increases genetic diversity may remain lo 2. Founder Effect - few individuals become isolated from large pop, allele freq in small founder pop will be dif from those in larger parent pop

Answer 39

small pops are more @ risk for extinction 1. lower heterozygosity=less adaptable 2. greater pairwise similarity=shared susceptibility to pathogens 3. deleterious alleles @ hi freq=hi genetic load

Answer 40

1. when p=0 or q=0 2. when population is at an intermediate equilibrium Only happens when either -heterozygotes are fittest=overdominace -heterozygotes least fit=underdominance