EvoMath is back from a long hiatus. In this edition I will
briefly touch on genetic drift and coalescence theory. Genetic
drift is the evolutionary force whereby allele frequencies
fluctuate due to chance because the alleles in a generation are
a random sample of the alleles in previous generation. To help
understand what I am talking about, consider a heterozygous
father, with genotype Aa. Under Mendelian heredity, he will pass
on the A allele 50% of the time and the a allele the other 50%
of the time. If he has only one child, then he clearly cannot
pass on both of his alleles, and thus one of those alleles–say
a–will be lost from his lineage. The remaining allele, A, will
then have “drifted” to 100% or “fixation.” If he has more
children, then he may pass on both of his alleles, but it is not
likely to be exactly at a 50:50 ratio. Genetic drift occurs
whenever a population has a finite size, and since all
populations are finite, it occurs in all populations. However,
in large populations it can be very wea