AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

GENOTYPIC VALUE

• Genotypic value may be calculated by taking a mean of a large population with same genotype raised under similar conditions.
• Here mean environmental deviation in the whole population is taken as zero.
• The genotypic value is partitioned into additive gene action, dominance and epistatis.
  • G = A + D + I

where

• G - Genotypic value
• A - Additive value
• D - Dominance deviation and
• I - Interaction or epistatic value

• Considering a single locus with two alleles, A₁ and A_2.

  • The genotypic value of
    • A₁ A₁ homozygote = +a
    • A₂ A₂ homozygote = –a and
    • A₁ A₂ heterozygote = d
  • The value of d of the heterozygote depends on the degree of dominance.
  • The degree of dominance may be expressed as d/a .