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

Causal Components of Variation

• The genetics of a metric character focuses on studying its variation by dividing it into components attributed to different causes.
• Variation is measured and expressed as variance, which is the mean of the required values when expressed as deviations from the population mean.
• Genotypic variance is the variance of genotypic values, while environmental variance is the variance of environmental deviations.
• The total variance, also known as phenotypic variance, is the sum of genotypic and environmental variances.
• Phenotypic variance is divided into additive, dominance, and interaction variants.
• The ratio of genotypic to phenotypic variance determines the importance of genotype in determining phenotypic value.
• In experimental populations, genotypic and environmental components can be estimated under certain circumstances.
• Environmental variance includes all non-genetic variances and cannot be eliminated experimentally.
• Additive variance, the variance of breeding values, is crucial for resemblance between relatives and response to selection.

Genetic Components of Variance

• Genotypic variance must be further divided into breeding value, dominance deviation, and interaction deviation to understand genetic properties.
• Additive variance, the variance of breeding values, is the key determinant of observable genetic properties and response to selection.
• Additive genetic variance is the only component that can be readily estimated from observations made on the population.

Genetic and Environmental Variance: A Detailed Overview

• Genetic variance refers to the variability in traits that is attributable to genetic differences among individuals.
• It can be broken down into additive genetic variance, dominance variance, and interaction variance.
• Additive genetic variance is the variance due to the sum of the effects of individual genes.
• Dominance variance arises from the interactions between alleles at the same locus.
• Interaction variance, while present, is relatively small and is often negligible in genetic studies.

• Environmental variance encompasses all variations in traits that are not caused by genetics.
• It can result from factors such as nutrition, climate, maternal effects, and errors in measurement.
• Environmental variance can introduce error and reduce the precision of genetic studies.
• Efforts to minimize environmental variance include careful experimental design and management.

• Maternal effects: These include influences of the mother on her offspring, such as nutrition.
• Error of measurement: Variance due to measurement errors, which can be significant for certain traits.
• Intangible variation: Unexplained variation that cannot be eliminated through experimental design.
• Developmental variation: Variation related to the development process and anatomical structures.

• Phenotypic variance can be divided into genetic and environmental components denoted by symbol V.
• This partitioning helps in understanding the contributions of genetics and the environment to observed traits.