Inbreeding & Health

Population health effects of inbreeding

Inbreeding increases the probability that recessive alleles (a) will come together as homozygotes (aa). It therefore increases the proportion of deleterious homozygotes in the population.

What is the ratio of recessive homozygotes in an inbred versus a non-inbred population?

If F = 0 (population not inbred) then
q²_exp / q²_obs = 1

If F > 0 (the population is inbred) & f(a) = q << 1 such that (p ~ 1), then
q²_exp / q²_obs = (q² + Fpq) / q² (q² + Fq) / q² = (q + F) / q F / q

Ex.: if q = 10^-4 & F = 0.01 = 10^-2 then F / q = 10²= 100

A small degree of inbreeding results in order-of-magnitude increases in the expected proportion of homozygotes for a rare deleterious allele.