Terminology Related to Mendelism

Mendel noticed that a single trait, such as stem height, could be expressed in two different ways - tall or dwarf - because the underlying gene can exist in alternative forms for the same trait, called alleles. An individual carrying two identical alleles of a gene is homozygous (for example TT or tt); an individual carrying two different alleles is heterozygous (for example Tt), and Mendel's non-true-breeding, hybrid plants were always heterozygous in this sense. When a gene has two alleles, the convention is to symbolise the dominant allele with a capital letter and the recessive allele with the corresponding small letter. An individual with two recessive alleles (tt) is homozygous recessive and shows the recessive phenotype (dwarf pea); an individual with two dominant alleles (TT) is homozygous dominant and shows the dominant phenotype (tall p …