Partitioning of Variation | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Components of Variation

Amount of variation is measured and expressed as variance. Variance is calculated as the mean of the squared values when expressed as deviations from the population mean.

Variance is partitioned into different components corresponding to specific values:

• Phenotypic variance (V_o): Variance of phenotypic values.
• Genotypic variance (V_A): Variance of genotypic values.
• Additive variance (V₂): Variance of breeding values.
• Dominance variance (V₁): Variance of dominance deviations.
• Interaction variance: Variance of interaction deviations.
• Environmental variance: Variance of environmental deviations.

Total variance (V_p) is the sum of these separate components:

• V_p = V₁ + V₂
• V_p = V₁ + V_A + V₂ + V_o

Components as Proportion of the Total:

• Partitioning variance into components helps in determining the relative importance of different factors influencing phenotype, such as heredity and environment.
• Estimating the role of heredity versus environment is crucial in understanding the determinants of phenotype.

Heritability and Genetic Variation

• Variation due to a specific source as a proportion of the total phenotypic variance.

• Heritability indicates the relative importance of genetics in determining phenotypic values.

• Hereditary can refer to being determined by genotype or transmitted from parents to offspring.
• The extent of heredity might differ based on whether it pertains to genotypic values or breeding values.

• VV_g expresses how much individual phenotypes are determined by genotypes.
• VV_a indicates the extent to which phenotypes are influenced by genes passed down from parents.