Discontinuously varying Traits Qualitative variations.

Traits with only a few possible phenotypes that fall into discrete classes; Examples. Pea Seed shape. Some traits, like pea seed shape, show discontinuous qualitative variations with two sharply distinct phenotypes, round or wrinkled 4 O‘clock flower colour can have three phenotypes, red, pink and white; ABO blood group system has four qualitatively different phenotypes A, B, AB and O. Continuously varying Trait.

Quantitative variation.

Traits, which have continuous or wide range of phenotypes between two extreme phenotypes. Examples. But many traits like height, weight, intelligence and skin colour in humans, and grain colour in wheat exhibits continuous quantitative variation over a range of many phenotypes. Mendel focused on traits that showed only two qualitatively different phenotypes which could be determined by just two alternate alleles of a single gene. Darwin observed small continuous variations within individuals of a population. Such a range of phenotypic spectrum of a trait cannot be traced to a single gene with two alleles. Even a few multiple alleles of a single gene cannot make such a wide range of phenotypes.

Polygenic traits.

A continuously varying trait is encoded by alleles of two or more different gene pairs found at different loci, all influencing the same trait in an additive way. These quantitative traits, are called polygenic traits