HWE: Non-random mating - 12 Flashcards
What are the 3 types of mating
- outcrossing
- inbreeding
- assortative mating
Define outcrossing
individuals related tend to avoid each other, non-random because deliberately avoiding each other
Define inbreeding
selfing in plants or mating with relatives.
includes consanguineous mating = mating between those that share a common ancestor/the same blood
Define assortative mating
where individuals choose mates that are similar (positive) or dissimilar (negative) in phenotype
What are the two conclusions of HWE
- that allele frequencies don’t change 2. that allele frequencies can be used to calculate genotype frequencies (through the equation)
How does inbreeding change the allele and genotype frequencies
allele frequencies don’t change, but genotype frequencies do, causing an increase in both homozygotes and a decrease in heterozygotes. This is because heterozygotes that self with themselves produce 1:2:1
What HWE assumption do the results of inbreeding violate
that allele frequencies can be used to calculate genotype frequency
Can non-random mating on its own result in evolution
no (ex. needs force of selection)
What is the inbreeding coefficient (F)
F = probability that two alleles are identical by descent
F = 0 no inbreeding
F = 1 selfing (only homozygotes), 0.5 (heterozygotes)
How to calculate probabilities of alleles being passed down
And = multiple
Or = add
define inbreeding depression (delta)
lower fitness in inbred populations because of increase in homozygosity and therefore increased expression of recessive alleles and recessive alleles are commonly deleterious
What does a positive or negative delta for inbreeding depression mean
negative delta = inbred individuals have a higher fitness (uncommon)
positive delta = outbred individuals have a higher fitness
Why is inbreeding bad (2)
increases frequency of deleterious alleles and decreases genetic variation
What are factors that lead to inbreeding (3)
decreased population size or density
isolation
hybridization and polyploidy
How can inbreeding be reduced (3)
migration
captive breeding (deciding who breeds with who)
inbreeding avoidance
What are 3 ways of inbreeding avoidance
mate choice (ex. MHC gene used to recognize if two individuals are closely related)
self-incompatibility genes (inability to produce zygotes after self pollination)
dispersal
(small population avoidance may not be possible)
What are the short and long term results of drift, migration, and inbreeding
short term = increased homozygosity due to drift or inbreeding can expose deleterious recessive alleles
long term = alleles are lost via drift which reduces the ability to adapt (to go or bad)
Ex. a reduce in heterozygous frequency is seen in one population of sea otters compared to the others, what are 3 possibilities for this heterozygote deficit
- inbreeding (assortative mating) 2. heterozygote inferiority 3. hidden population structure
Explain how assortative mating can cause heterozygote deficit
AA x AA = AA
aa x aa = aa
Aa x Aa = 1:2:1
homozygotes will increase and heterozygotes will decrease
Explain how heterozygote inferiority can cause heterozygote deficit
the homozygotes have a higher survival rate that could be due to a difference in phenotype or genotype quality
Explain how hidden population structure can cause heterozygote deficit
Wahlund Effect
Although different genotypes are living in the same area, for some reason they still aren’t breeding together and random mating isn’t occurring. The same phenotypes are mating with one another and there is a hidden population structure!
