Mutation Rates Increase in Organisms Under Stress
OK, well, geez- someone was just asking for evidence for increased mutation rates after the Flood, so here it is:
Mutations induced by stress contribute significantly to spontaneous mutation
I am pretty sure the Flood event would be pretty stressful, as would the period of re-occupation.
So several HUNDRED alleles out of several BILLION attempts would seem easily achieved given known mechanisms of genetic recombination, inragenic recombination, insertions, deletions, inversions and stress-induced mutagenesis.