Considering “p” the number of phenotypical forms and “a” the number of involved alleles of the polygenic inheritance. The formula p = 2a + 1 is then applied.
(Many times it is not possible to determine precisely the number of phenotypical forms, p, due to the multigenic feature of the inheritance, since often the observed variation of phenotypes seems to be on a continuum or the trait suffers environmental influence.)
