Single- versus Multi-locus trait distributions
A
trait
determined by a single locus with two alternative alleles (A and a) occurs in three (31) genotypic classes (AA, Aa,
and aa). These
correspond to three distinct phenotypes, if A is co- or semi-dominant
with a. As the number
of contributing loci increases, e.g., from five loci (A1 
A5) with 35 = 243
possible phenotype classes or n loci with 3n,
the character
distribution becomes essentially continuous, and follows the
normal distribution.
A5) with 35 = 243
possible phenotype classes or n loci with 3n,
the character
distribution becomes essentially continuous, and follows the
normal distribution.