Lecture 10: non-random mating

Question 1

Types of non-random mating (3)

Answer 1

-Negative assortative mating
- positive assortative mating
-Inbreeding

Note can change / overlap depending on selection

Question 2

Negative assortative mating (3)

Answer 2

– opposites attract (black with white)
– maintains polymorphisms at relevant loci (i.e. feather color but not eye color in birds)
-relatively rare

Question 3

Positive assortative mating (3)

Answer 3

-Same same (white with white)
-Increases homozygosity at relevant loci (i.e. feather color but not eye color in birds)
-more common

Question 4

inbreeding (3)

Answer 4

-Increases homozygosity across entire genome
– Can have important evolutionary consequences
-Allele frequencies do not change but genotype frequencies do

Question 5

Inbreeding depression (sigma) (3)

Answer 5

-Sigma = 1 - (ωinbred / ωoutbread)

-inbreeding increases expression of all recessive alleles

-increased expression of deleterious alleles can reduce fitness in inbreeding populations

-increasing proportion of homozygotes increases the frequency of deleterious recessive phenotypes

Question 6

Purging of deleterious alleles (4)

Answer 6

-in Sustained inbreeding Deleterious recessives will be exposed to selection because homozygotes are more common, causing Deleterious recessives to may be “purged” from the population.

-May be effective when increased inbreeding is gradual and population size is maintained However, small populations experience both drift & inbreeding

-mildly deleterious alleles are more likely to be fixed by drift when N is small (s &laquo_space;1/2N)

• this may increase sigma, further reduce N, and cause fixation of additional deleterious alleles

Question 7

Genetic load

Answer 7

Accumulation of deleterious alleles

Question 8

Extinction vortex(2)

Answer 8

-Aka genetic load or mutational meltdown

-Small population -> inbreeding and genetic drift -> loss of genetic viability -> reduction in individual fitness and adaptability -> lower reproduction and higher mortality -> smaller population -> …….

Question 9

Inbreeding overall (4)

Answer 9

1) Increases homozygosity across genome

2) Populations with high “genetic load” experience inbreeding depression.

3) Inbreeding can sometimes purge deleterious alleles
.
4) Inbreeding is often associated with smallpopulations and genetic drift.