Phenotypic Assortative Mating | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Introduction

Assortative mating is a non-random mating pattern that plays a significant role in shaping genotype frequencies within populations. There are two types: ancestral descent-related mating and genotype-based mating, known as assortative mating. This phenomenon has implications for the distribution of alleles and can impact various traits, such as stature and intelligence.

Types of Assortative Mating

Ancestral Descent-Related Mating:

• Increases frequencies of homzygotes at all loci.

Genotype-Based Mating (Assortative Mating):

• Individuals preferentially mate based on their genotypes at specific loci. 
• Can be either assortative (mates of the same phenotype) or disassortative (mates of different phenotypes).

Consequences of Assortative Mating

• Genotype frequencies are affected, with an increase in homozygotes and a reduction in heterozygotes.
• Populations tend to be partially divided into groups with more frequent mating within than between groups.
• Over successive generations, the population approaches an equilibrium with constant genotype frequencies.

Human Populations and Assortative Mating:

• Human populations exhibit assortative mating in various traits like stature and intelligence.
• Mating choices might not always be deliberate but can lead to correlations between phenotypic values in mated individuals.

Heritability and Assortative Mating

• The degree of assortative mating is expressed as the correlation (r) between phenotypic values of mated individuals.
• Genetic consequences include an increase in additive variance, influencing heritability.
• Ambiguity in heritability interpretation under assortative mating.

Genetic Effects and Other Aspects

Increase in Additive Variance:

• Resulting correlation between breeding values causes an increase in additive variance.
• Correlations between relatives also increase, influencing heritability estimates.

Temporal Aspects:

• Effects are not immediate; several generations following random mating are needed to reach equilibrium.
• Dependent on the number of loci influencing the trait.

Dominance Variance:

• Effects on dominance variance are small and may be neglected.
• Attention focused on pair matings producing full families in the progeny, disregarding linkage.

Precision of Heritability Estimates:

• Assortative mating increases precision in estimating heritability.
• Reduction in standard error due to increased variance of mid-parent values.
• Effects observed in the regression of offspring on single parent and full-sib correlation.

Conclusion

Assortative mating, whether ancestral or genotype-based, has substantial implications for genetic outcomes and heritability estimates within populations. Understanding these patterns is crucial for comprehending the dynamics of genetic traits in diverse populations.