The number of alleles that can be maintained in a finite population
Genetics, 49 (4):
725--738 (1964)Abstract
I but rather a population of different isoalleles that are indistinguishable by
any ordinary procedure. With hundreds of nucleotides, each presumably cap-
able of base substitutions and with additional permutations possible through se-
quence rearrangements, gains, and losses, the number of possible gene states
becomes astronomical. It is known that a single nucleotide substitution can have
the most drastic consequences, but there are also mutations with very minute
effects and there is the possibility that many are so small as to be undetectable.
It is not the purpose of this article to discuss the plausibility of such a system
of isoalleles, or the evidence for and against. Instead, we propose to examine some
of the population consequences of such a system if it does exist. The probability
seems great enough to warrant such an inquiry.
If a large number of different states can arise by mutation, this doesn't neces-
sarily mean that a large fraction of these would coexist in a single population.
Some will be lost by random drift and others may be selectively disadvantageous.
On the other hand, some may persist by being beneficial in heterozygous
combinations.
We shall consider three possibilities: ( 1 ) A system of selectively neutral
isoalleles whose frequency in the population is determined by the mutation rate
and by random drift. (2) A system of mutually heterotic alleles. ( 3 ) A mixture
of heterotic and harmful mutants.
