Lecture 9: Inbreeding and Assortative Mating Flashcards
What is meant by “identity by descent (IBD)”?
The idea that there are chunks of your genome that are identical chunks of other people’s genomes due to a common ancestor.
What is the inbreeding co-efficient (F)?
A number that describes the fraction of the genome we expect to be homozygous given a certain level of inbreeding.
How do we calculate the inbreeding co-efficient (F)?
F = Σ 2 x 0.5^n summed over each closed loop in the pedigree, where n is the number of transmissions of an allele in the loop.
What is the inbreeding co-efficient if parent-offspring or full siblings mate?
F = 0.25 (25% of the genome homozygous)
What is the inbreeding co-efficient if…
- Grandparent-grandchild mate?
- Half siblings mate?
- Double first cousins mate?
0.125 (12.5% of the genome homozygous)
What is the inbreeding co-efficient if first cousins mate?
0.0625 (6.25% of the genome homozygous)
What is the inbreeding co-efficient if second cousins mate?
0.015625 (1.5625% of the genome homozygous)
What is inbreeding depression?
The concept that inbreeding leads to reduced fitness.
How does the probability of being homozygous differ in an inbreeding scenario (i.e., Hardy-Weinberg proportions under inbreeding)?
For unrelated individuals = p^2 + q^2
This increases to: p^2 + q^2 + 2pqF (for related individuals)
What is the Hardy-Weinberg formula for related (inbred) populations?
p^2 + pqF + 2pq - 2pqF + q^2 + pqF = 1
What effect does an increasing inbreeding co-efficient (F) have on the HW plot?
We see an increasing level of homozygotes and we see a loss of heterozygotes.
What is assortative mating?
Mating based on phenotypic preference (similarity/dissimilarity etc.).
What does assortative mating lead to?
Increased homozygosity.
What is disassortative mating?
Negative assortative mating (e.g., heterostyly in primroses).
What does disassortative mating lead to?
Increased heterozygosity.
