Quantitative Genetics II

Question 1

natural selection happens if…

Answer 1

• traits are variable
• the variable traits are heritable
• the variable, heritable traits affect an individual’s probability of surviving and leaving offspring

Question 2

selection differential

Answer 2

• S
• the difference in mean trait values before & after selection

Question 3

example of a selection differential

Answer 3

• Bumpus sparrows
• snow storm hit New England
• sparrows collected, all near dealth
• measured 9 characters on all of the birds

Question 4

what happens if there is selection and heritable variation?

Answer 4

an evolutionary response to selection

Question 5

breeders equation

Answer 5

R = h^2S

Question 6

how to calculate the relative fitness for quantitative traits

Answer 6

absolute fitness / mean fitness

Question 7

SD =

Answer 7

square root of variance

Question 8

slope =

Answer 8

selection gradient (beta)

Question 9

what does the linear selection gradient quantify?

Answer 9

the impact of selection on the trait mean

Question 10

what does the non-linear gradient quantify?

Answer 10

the impact of selection on trait variance

Question 11

negative y indicates …

Answer 11

stabilizing selection

Question 12

positive y indicates …

Answer 12

disruptive selection

Question 13

what happens if multiple traits are included in the calculation of selection gradients?

Answer 13

one can separate the effects of direct selection from indirect selection

Question 14

correlational selection

Answer 14

when natural selection favors specific combinations of traits

Question 15

examples of correlated response to selection

Answer 15

• increased butter fat in cow milk, decreased milk yield
• increase back fat in pigs, decrease body length

Question 16

genetic correlations

Answer 16

correlations among phenotypic characters due to pleiotropy or linkage disequilibrium

Question 17

pleiotropy

Answer 17

a phenotypic effect of a single gene on more than one trait

Question 18

is pleiotropy common?

Answer 18

yes

Question 19

pleiotropy example

Answer 19

• frizzle mutation in chickens
• feathers curl outward instead of lying flat against the body

Question 20

linkage disequilibrium

Answer 20

a non-random association between the alleles present at two or more loci

Question 21

linkage disequilibrium when at equilibrium

Answer 21

the frequency of alleles at 2 or more loci occurring together equal to the products of their individual probabilities

Question 22

linkage disequilibrium when not at equilibrium

Answer 22

the frequency of alleles at 2 or more loci occurring together does not equal the product of their individual probabilities

Question 23

how to calculate linkage disequilibrium

Answer 23

D = gAB gab - gAb gaB

Question 24

the minimum value of D

Answer 24

0

Question 25

the maximum values of D

Answer 25

0.25 and -0.25

Question 26

causes of linkage disequilibrium

Answer 26

• physical linkage
• natural selection

Question 27

causes of linkage disequilibrium: physical linkage

Answer 27

LD decays proportional to the recombination rate (r)

Question 28

causes of linkage disequilibrium: natural selection

Answer 28

natural selection can build up LD, but it decays quickly, loci are on different chromosomes

Question 29

a genetic fingerprint of natural selection and an example of linkage disequilibrium

Answer 29

• 70% of adults cannot drink milk
• we use the gene lactase to break down lactose when we are children
• after a body stops making lactase, you can become lactose intolerant

Question 30

selective sweep

Answer 30

when an adaptive mutation is quickly moved to fixation in a population, or spreads geographically due to strong selection

Question 31

consequence of directional selection

Answer 31

selective sweeps

Question 32

genetic hitchhiking

Answer 32

with a selective sweep, genetically linked regions also increase in frequency

Question 33

what do genetic correlations lead to?

Answer 33

correlated responses to selection