Exam 2

Question 1

Explain why natural selection is most rapid when it acts on common recessive alleles (and rare dominant alleles).

Answer 1

• When a recessive allele is rare, most copies are hidden in heterozygotes and protected from selection.
• So as A2 becomes less common, natural selection acts more slowly.

Question 2

define overdominance

Answer 2

• heterozygote advantage
• heterozygotes have higher fitness than homozygotes

Question 3

overdominance - predict how it should affect allele and genotype frequencies

Answer 3

natural selection will produce equilibrium allele frequencies and fixation will not occur

Question 4

overdominance example

Answer 4

• Sickle cell and Mukai and Burdick fruit fly experiment
• both alleles meet at a certain number (no fixation)

Question 5

define underdominance

Answer 5

• homozygote advantage
• homozygotes have higher fitness than heterozygotes

Question 6

underdominance - predict how it should affect allele and genotype frequencies

Answer 6

natural selection will fix one allele or the other depending on which is more common

Question 7

underdominance example

Answer 7

• Foster et al. fruit fly experiment
• 2 alleles goes to fixation
• starting frequency affects which one becomes fixed

Question 8

what happens in negative frequency dependent selection (NFDS)

Answer 8

Rare genotype more fit than common genotype

Question 9

NFDS - predict how it should affect allele and genotype frequencies

Answer 9

natural selection will produce equilibrium allele frequencies and fixation will not occur

Question 10

NFDS example

Answer 10

• Gigord et al. orchid experiment
• when yellow trait is rare, it has a higher fitness
• when it is common, it has lower fitness
• frequency of yellow morph and reproductive success has a neg. correlation

Question 11

Explain why mutation on its own is a weak evolutionary mechanisms.

Answer 11

• mutation rates are too small
• needs to act on selection for it to become rapid

Question 12

how is mutation-selection balance is a potential explanation for the high-frequency of a deleterious allele in a population

Answer 12

• mutation-selection balance
• The frequency of a deleterious allele can remain at equilibrium if the opposing mechanisms of selection and mutation are equal

Question 13

Explain how genetic drift affects heterozygosity, genotypic diversity, and allelic diversity in a focal population

Answer 13

decreases all three

Question 14

For a focal population that is evolving in response to genetic drift, you should be able to predict that likelihood that a particular allele will drift to fixation.

Answer 14

it will be the starting/initial frequency

Question 15

Understand what neutral theory is, three predictions it makes (that are supported)

Answer 15

1. Beneficial mutations are rare, start at low frequency, and are often lost—uncommon—can be fixed positive selection
2. Deleterious mutations are removed by purifying selection (so don’t contribute to evolution)
3. Neutral mutations rise and fall b/c drift

Question 16

why is neutral theory an important tool (detect selection).

Answer 16

• comparing ratio of nonsynonymous vs.
  synonymous substitutions
• N/S<1 = deleterious
• N/S=1 = neutral
• N/S>1 = positive

Question 17

how does inbreeding affects allele and genotype frequencies using a selfing example.

Answer 17

• no change in allele frequencies but change in genotypic frequencies
• Homozygotes increase in frequency
• Heterozygotes decrease in frequency

Question 18

explain why is nonrandom mating should not be considered an “Evolutionary Mechanism”

Answer 18

• allele frequencies do not change (conclusion 1 is not violated) but it violates conclusion 2 of HW bc it cannot be predicted using the equation

Question 19

explain inbreeding depression

Answer 19

effect deleterious recessive alleles have on the average fitness of offspring in the population

Question 20

why does inbreeding depression occur as well as examples of fitness consequences

Answer 20

By increasing the proportion of homozygotes, inbreeding increases the frequency with which deleterious recessive (loss-of-function) alleles affect phenotypes –there are more “aa” phenotypes in the population

Question 21

define conservation genetics

Answer 21

application of population genetics to understand and reduce the risk of population and species extinctions

Question 22

recognize how/why conservation genetics fits in with chapters 6 & 7 (drift and gene flow)

Answer 22

• populations that need conservation are small due to extinction
• makes them more vulnerable to drift and gene flow

Question 23

list and explain 3 processes that cause LD

Answer 23

1. selection
2. drift
3. migration

Question 24

be able to explain how sex restores LE.

Answer 24

• Genetic recombination randomizes genotypes at one locus with respect to genotypes at another
• reduces LD

Question 25

Understand how sex increases genetic variation.

Answer 25

- Genetic Recombination (crossing over) - Creates chromosomes with new combination of alleles for all genes one a chromosome

Question 26

describe the Red Queen Hypothesis

Answer 26

individuals must continually evolve new adaptations in response to other organisms adaptations to avoid extinction

Question 27

red queen hypothesis - how does it explains the value of sex

Answer 27

sex allows organisms to 'outrun' extinction through the creation of new alleles via crossing over

Question 28

describe Mueller’s ratchet in detail.

Answer 28

- Asexual populations occasionally sustains deleterious mutations - If the zero mutation group is small, chance events may cause its extinction - Then the one mutation group will now have highest fitness - Loss of a group by drift is easier than is replacement by backmutation

Question 29

generally describe what QTL mapping is and what it is used for

Answer 29

- a statistical analysis - used to identify which molecular markers lead to a quantitative change of a particular trait

Question 30

distinguish “broad-sense” from “narrow-sense” heritability

Answer 30

- broad-sense = the proportion of the total variance that is due to genetic variance so h^2 = var(P)/var(G) - narrow-sense = proportion of total variance in a trait that is due to additive genetic variance so h^2 = var(A)/var(G)

Question 31

define the terms in this equation: Var (P) = Var (A) + Var (I) + Var (D) + Var (E).

Answer 31

- var(A), var(I), and var(D) = genetic variance - var(P) = variation in phenotype - var(A) = additive genetic variance - var(I) = variance in Interactions or epistasis - var(D) = variation in dominance - var(E) = environmental variance

Question 32

explain all of the terms of the breeder’s equation

Answer 32

- equation: R = h^2*S - R = response to selection - h^2 = heritability S = selection differential

Question 33

to define each of the 3 ways of selection, give a hypothetical example of each, and be able to graph trait distributions and selection curves (case study slides).

Answer 33

- disruptive: extreme traits are selected for - stabilizing: intermediate trait is selected for - directional: one extreme is selected over the other extreme

Question 34

explain what an adaptive hypothesis is and list the components of an adaptive explanation

Answer 34

- an explanation for the evolution of a trait from an ancestral condition that describes the specific environmental condition that selected for the trait (the selective pressure) - should explain function and fitness

Question 35

why might a trait evolved from an ancestor that did not possess that trait.

Answer 35

- drift - mutation - vestigial - pleiotropy (genes interacting w other genes, one is adaptive and another is not) - constraints and trade-offs

Question 36

explain how observational studies can be used to evaluate aspects of an adaptive hypothesis.

Answer 36

- it can address function only if there is a significant relationship between traits and fitness - if that is the case, drift can be rejected - cannot address phylogenetic history

Question 37

observational studies - giraffe example.

Answer 37

- researchers tested theory that giraffe evolved long necks to eat off leaves - observational studies show that giraffes do not eat at their maximum height

Question 37

observational studies: giraffe - what is another explanation for their necks

Answer 37

adaptation for male-male combat

Question 38

explain how experimental studies can be used to evaluate aspects of an adaptive hypothesis

Answer 38

- can address function AND causation if designed well - can reject drift if there is a significant relationship between traits and fitness

Question 39

experimental studies - flower marker example

Answer 39

hypothesis: If pollinators find well-marked flowers more attractive (function), the plants that display them should enjoy higher reproductive success (fitness)

Question 40

experimental studies: flower marker example - how did they conduct the study

Answer 40

- used black ink to fill in the white arrowheads on experimental flowers - results showed that pollinators visited the control more (matches hypothesis)

Question 41

explain how the comparative method can be used to evaluate aspects of an adaptive hypothesis

Answer 41

- cannot address function - can reject drift if there is a significant relationship between the traits that species have and the environment those species inhabit - phylogenetic history can be addressed instead of current environmental conditions as a good explanation for trait variation among lineages

Question 42

comparative studies - Phylogenetically Independent contrasts

Answer 42

the name of the main statistical tool people use to take phylogenetic relationships into account when applying the comparative method

Question 43

comparative studies - explain why phylogenetic studies are a necessary complement to the comparative method

Answer 43

allows for more accurate hypotheses on how traits evolved due to selection pressures rather than inheritance alone

Question 44

describe some of the assumptions that are inherent to parent/offspring regressions

Answer 44

1. assumes that the trait variance is primarily due to additive genetic effects 2. environmental factors shared between parents and offspring don’t significantly impact the trait. 3. parents do not selectively invest in offspring based on their trait values 4. a consistent environment between the parental and offspring generations.

Question 45

discuss the limitations of estimating heritability using parent/offspring regression

Answer 45

1. Shared environmental factors can be difficult to completely rule out, making it challenging to disentangle genetic contributions from environmental ones 2. Limited to Linear Additive Effects 3. over- or Underestimation of Heritability 4. it doesn’t directly account for how selection pressures might act on the trait across generation

Question 46

true or false: a heritability of 0.6 indicates that 60% of the trait in an animal is determined by its genes

Answer 46

- false - 60% of the variation in the trait within a population can be attributed to genetic differences among individuals - the remaining 40% of the variation is due to environmental factors or other influences.

Question 47

true or false: if a trait has no heritability (h^2 = 0), that means the trait is not determined by genes

Answer 47

- false - there is no genetic variation in the population for that trait - all individuals in the population have the same genetic contribution to the trait - any differences we observe are due to environmental factors.

Question 48

is it possible for heritability to be very low if var(P) is not explained by environmental variation

Answer 48

- false - h^2 can only be low if a large portion of the phenotypic variance is due to environmental effects or other non-genetic factors

Question 49

if a trait has a heritability as one does that mean the environment is constant

Answer 49

- no - for the population in question, environmental differences are not influencing tat particular trait's variation.