13.. Other Evolutionary Mechanisms

Nonrandom mating

Negative Assortative Mating: mating with those that have different traits / genotypes (outbreeding)

Positive Assortative Mating: mating with those that have similar traits / genotypes (inbreeding)

Allele States

Alleles can be identical by descent (same allele coming from the same ancestor)

Alleles can be identical by state (same allele coming from different ancestors)

Inbreeding Coefficient (F)

Measures the degree of inbreeding; chance of an allele being identical by descent

- Ranges from 0 to 1

- 1 is self-fertilization, very high inbreeding

Inbreeding depression

Decrease in survivorship and fitness due to inbreeding

Higher chance of expression of deleterious recessive alleles

Inbreeding in Hardy Weinberg

f(AA) = p^2 + Fpq

f(Aa) = 2pq - 2Fpq

f(aa) = q^2 + Fpq

Inbreeding decreases the number of heterozygotes and increases homozygotes

*Inbreeding does not change allele frequencies*

Genetic Rescue

Genetic rescue is a technique to increase the genetic diversity of a population by crossing them with individuals of a distinct population.

The Florida panther population was severely reduced and inbreeding depression was exhibited. They were mixed with a different panther species.

Black-footed ferrets have an extremely low population. Elizabeth Ann is a clone from a skin cell of a ferret found in 1988 to try to increase the small population's diversity.

Mutation

All new alleles arise by mutation

- Increase variation within and between populations

- Mutation rate = number of mutations per biological unit

Forward mutation:

Δq = 𝜇p where 𝜇 is the mutation rate and p is the frequency of the dominant allele

After finding Δq (the change in the frequency of the recessive allele), you need to add it to q (the frequency of the recessive allele) to find the new allele frequency

Gene Flow (Migration)

Movement of alleles into an existing population

- increases variation within groups

- decreases variation between groups

Bidirectional flow will eventually lead to an equilibirum

Unidirectional flow:

Δq = m(qI , donor - qII, receiver) where m is the migration rate

**Δq can be negative**

After finding Δq, you need to add it to q (the frequency of the recessive allele) to find the new allele frequency

Relative Fitness (W)

Contribution of individuals with one genotype compared with the average contribution of all individuals and genotypes in the population

The effect of mechanisms on genetic variation

Increase within pop

- mutation ; migration; natural selection

Decrease within pop

- genetic drift; natural selection

Increase between pop

- mutation; genetic drift; natural selection

Decrease between pop

- migration; natural selection

Which agent(s) of evolution increase genetic variation between populations but not within populations? Select all that apply.

a. Mutation

b. Genetic Drift

c. Natural Selection

d. Migration

a. Mutation

b. Genetic Drift

c. Natural Selection

A dominant allele (D) mutates into the recessive allele (d) at a rate of 1 × 10^-3. Assuming no other evolutionary forces are at work and the initial frequency of d is 0.5, what would be the frequency of the recessive allele the next generation?

a. 0.5

b. 0.0005

c. 0.505

d. 0.5005

d. 0.5005

The rate of D -> d is 1 * 10^-3

q = 0.5

1 - q = p -> 1 - 0.5 = 0.5 = p

Δq = 𝜇p

(1 * 10^-3) * 0.5 = 0.0005 = Δq

q + Δq = new q

0.5 + 0.0005 = 0.5005

If the frequency of a recessive autosomal allele that causes a blood disease is 0.1, what is the frequency of individuals with the disease in a population if that population has an inbreeding coefficient of 0.15?

a. 0.18

b. 0.0235

c. 0.153

d. 0.8235

b. 0.0235

q = 0.1

1 - q = p -> 1 - 0.1 = 0.9 = p

F = 0.15

f(aa) = q^2 + Fpq

(0.1 ^ 2) + (0.15 * 0.9 * 0.1) = 0.0235

The frequency of q in the mainland is 0.3, and the frequency of q in the island population is 0.7. If the migration rate from the mainland into the island is 0.4, what will be the frequency of q on the island in the next generation?

a. 0.54

b. -0.16

c. 0.86

d. 0.16

a. 0.54

migration from mainland (donor) to island (receiver)

Δq = m(qI , donor - qII, receiver)

migration rate = 0.4

qI = mainland = 0.3

qII = island = 0.7

(0.4) * (0.3 - 0.7) = -0.16

island + Δq = new frequency

0.7 + (-0.16) = 0.54

If an allele (f(aa) = 0.5) in a population decreases in frequency over a long period of time, taking 100 years to reach a frequency of 0, which agent of evolution is likely to be the cause? The curve is a wide backwards L shape. The frequency had reached 0.1 by 10 years.

a. Genetic Drift

b. Natural selection

c. Mutation

d. Assortative Mating

e. Inbreeding

b. Natural selection; It is slowly selecting against the allele in one direction

- Genetic drift would show a much more erratic pattern

- Mutation is very very slow; It would take a much longer time to reach 0.

- Assortative mating doesn't tend to change the allele frequency.

- Inbreeding is a type of assortative mating and does not change allele frequency