Question

Why are two letters (such as TT,Tt,tt) used to denote the character of height?

Answer 1

Two letters are used to denote because one letter which is small denotes recessive, and ine letter which is capital denotes dominant character. Thus dominant trait expresses itself even when a heterozygous genotype is present , but recessive character expresses itself only when a homozygous genotype containing both small letters are present.