Law of Dominance

1. Law of Dominance :

The Law of Dominance addresses what happens to a pair of contrasting factors when they are brought together in a hybrid. In both Mendel's monohybrid and dihybrid crosses, each phenotypic character is controlled by a discrete factor, and when two different forms of that factor are paired in the same individual, one of them — the dominant factor — masks the expression of the other (recessive) factor completely. This is why an F1 monohybrid (e.g., Tt) looks identical to the dominant parent even though it carries the recessive allele silently, and why that hidden recessive trait resurfaces only in F2, once dominant and recessive alleles have had a chance to combine as tt.

Formally: 'When two homozygous individuals with one or more sets of contrasting characters are crossed, the alleles (characters) that appear in the F1 are dominant, and those which do not appear in the F1 are recessive.' It is worth noting — as the chapter itself flags — that this law is not truly universal: cases such as incomplete dominance and co-dominance (covered later in this chapter) show alleles that do not simply mask one another but instead blend or express together. …