[ genetic copies of an allele in a common ancestor ]

[Note than alleles can be identical by allelic state without being identical by descent]

**F** is also the *proportion*
of the population that is inbred (has two alleles identical by descent).

**What is the effect of inbreeding on
genotype proportions?**

In the *absence* of inbreeding,
expected
f(**AA**) = p^{2}

f(**AB**) = 2pq

f(**BB**) = q^{2}

In the *presence* of inbreeding,

f(**AA**) = (1-F)(p^{2})
+
(F)(p)(1) = p^{2} - Fp^{2} + Fp
= p^{2} + Fp(1-p) = **p ^{2}
+ Fpq**

the expected frequency of

A fraction (

a fraction

Since they are inbred,

f(**AB**) = (1-F)(2pq) +
(F)(0)
= 2pq - 2Fpq = **2pq
(1 - F)**

** **
[A fraction **(1-F)** of the
population
is not inbred:

the
expected frequency of **AB** heterozygotes among these is **2pq**.

A fraction (**F**) of the population is inbred:

among
these, *none* can be heterozygotes, since both alleles are
identical.]

f(**BB**) = (1-F)(q^{2}) +
(F)(q)(1)
= q^{2} - Fq^{2} + Fq = ** q ^{2}
+ Fpq**

[Same logic as for f(

Text material © 2001 by Steven M. Carr