Strains may differ in Segregating Genes

A small colonies of rumbunnies was discovered in the Hunt's Mill Park in Clinton New Jersey. It is distributed up and down the South Branch of the Raritan River.  In measurements of 1650 rumbunnies the mean number of chin whiskers was 16.64.  The mean difference was shown to be genetic in laboratory studies. The mean average is below the expected number of whiskers for the "worst" genotype in the Pine Barrens, Carteret and Water Gap Populations.  Additional work revealed that approximately 3/4 of the rumbunnies had 20 to 32 chin whiskers while about 1/4 had no chin whiskers.  

With additional work, researchers discovered a third gene - the D gene which is completely dominant.  Individuals which have the DD or Dd genotype have at least 20 chin whiskers depending on the genotype at the A and B loci. Individuals with the dd genotype however, have not chin whiskers.  dd masks the effect of the A and B loci.

In the Clinton population the frequency of d was .6.  Since rumbunnies approached Hardy-Weinberg equilibrium the frequency of the dominant phenotypes was (p² + 2pq) = .64 and of the recessive phenotype (q²) = .36

Take Home Lesson: Comparisons of the three strains from Carteret, Pine Barrens and Water Gap did not tell the full story of the inheritance of chin whiskers since those populations were homozygous "fixed" for the D allele.  Strain comparisons are really only accurate for the strains being compared and may only carefully be extended to other strains.