Ch07

Question 1

List the Hardy-Weinberg assumptions

Answer 1

(1) No Natural Selection
(2) Random mating
(3) No mutation
(4) No migration
(5) Infinitely large population

Question 2

List the Hardy-Weinberg conclusion

Answer 2

(1) Allele frequencies do not change through time
(2) Given random mating, equilibrium genotype frequencies can be predicted
(3) Equilibrium frequencies will be reached in one generation

Question 3

Why is it that in the HW model allele frequencies are at a neural equilibrium, while genotype frequencies are at a stable equilibrium?

Answer 3

Because p & q can take any value

Because there is an equilibrium genotype frequency for every p value

Question 4

Why dominant alleles would not replace recessive alleles in a population over time?

Answer 4

there is a BIG difference between allele Expression & Transmission

Question 5

Define selection coefficient (s)

Answer 5

selection strength for or against a particular phenotype or genotype

Question 6

What happens when s is larger

Answer 6

NS would be stronger, alleles frequencies change faster, & favored allele reach fixation faster

Question 7

Both fitness & selection coefficient are context specific, so they are…

Answer 7

expected to vary among populations & time

Question 8

Define Frequency-independent selection

Answer 8

Genotype fitness is NOT influenced by its frequency in population

Question 9

Define Directional selection

Answer 9

Selection where one allele is consistently favored over other
*CDA1A2>DA1>RA1

Question 10

Define Overdominance

Answer 10

when heterozygote has the highest fitness. stable equilibrium
ex. Sickle-cell anemia

Question 11

Define Underdominance

Answer 11

where heterozygote has the lowest fitness. Has 2 possible fixation. unstable equilibrium

Question 12

Define Frequency-dependent selection

Answer 12

Genotype fitness is influenced by its frequency in the population

Question 13

Explain Positive frequency-dependent selection

Answer 13

as frequency increases, fitness increases. one allele will eventually be fixed & the other will be lost depending on the initial allele frequencies
ex. flat snail

Question 14

Explain Negative frequency-dependent selection

Answer 14

as frequency decreases, fitness increases. When the frequency of one type becomes greater than the other, frequency-dependent selection brings population back to a 50–50 split. This causes a fluctuation between two phenotype over time
ex. fish bite

Question 15

Explain Mutation–selection balance

Answer 15

At equilibrium, the rate of mutation from favored A1 alleles to disfavored A2 alleles (μ) is balanced by selection against disfavored A2 alleles (s). This does not eliminate disfavored A2 alleles
Ex. Familial adenomatous polyposis

Question 16

Explain Effects of Non-random mating

Answer 16

Does not change allele frequencies, but changes genotype frequencies from what is expected under the HW model. It disrupts HW equilibrium

Question 17

Define Assortative mating

Answer 17

individuals tend to mate with those of the same genotype or phenotype. Frequency of heterozygous individuals decrease & those of homozygotes increase

Question 18

Define Disassortative mating

Answer 18

individuals tend to mate with those of different genotypes or phenotypes. Frequency of heterozygous individuals increases & those of homozygotes decrease

Question 19

What effects does Inbreeding have on allele frequencies?

Answer 19

In the absence of any other evolutionary forces allele frequencies remain the same

Question 20

Define Inbreeding depression

Answer 20

occurs when the offspring from matings between genetic relatives have reduced fitnesses

Question 21

What effects does Migration have on allele frequencies?

Answer 21

Excluding all other evolutionary forces, migrations tend to homogenize allele frequencies