Methods of Symbolisation in Genetics

Methods of Symbolisation:

1. Classical Method: Mendel used the English alphabet to represent the factors. The first letter of the dominant character is often used to designate the character, as T for tallness, represents the dominant character and the small letter (t) represents its recessive character (dwarfness). According to this system, the genotype of a dwarf will be tt and homozygous tall will be TT and heterozygous tall will be Tt.

2. Modified Classical Method: It is very often the letter is chosen on the basis of a mutant character. The mutant character when recessive is designated by a small letter and its wild or normal character is represented by a capital letter.

Example: Albinism in man is recessive mutant. It is represented by ‘a’ whereas the normal skin color is represented by ‘A’. The genotype of:

    i. Albino (Nonpigmented) = aa
    ii. Normal skin color (Pigmented) – Homozygous = AA
    iii. Normal skin color (Pigmented) – Heterozygous = Aa

3. Wild Type Symbols: Another method of using the symbols includes the use of +sign for the wild type and its mutant is represented by the first letter of the mutant character either as capital or small depending upon whether the mutant is dominant or recessive.

Example: In tall and dwarf characters of pea plants the wild or tall character is represented as +/+ and dwarf as d/d. The genotype of F1 hybrids will be represented by +/d/.