Basic Concepts of Coalescence
A population in Generation t
is a mixture of haploid individuals, in
two different allelic states (red and black), that create
offspring at random, which then occur in Generation t+1.
In a sample of three individuals drawn from generation t+1
(yellow circle),
two have the same parent in generation
t, while the third has a different
parent. The two individuals are said to coalesce: they
"come together" backward
in time to a single parent in the previous
generation.
Note that another sample of three individuals (blue circle) drawn from generation t+1 might also include two with the same allele (both red, or both black), but not as the result of coalescence. This pair may look the same, but the first is the result of Identity by Descent and the second simply represents Identify by Allelic State.
Note that another sample of three individuals (blue circle) drawn from generation t+1 might also include two with the same allele (both red, or both black), but not as the result of coalescence. This pair may look the same, but the first is the result of Identity by Descent and the second simply represents Identify by Allelic State.
Figure © 2013 by Sinauer; Text material © 2022 by Steven M. Carr