6.3 Non-random mating and assortative mating

Non-random mating shakes up population genetics. It occurs when individuals choose mates based on specific traits, leading to assortative mating, inbreeding, and sexual selection. These patterns disrupt Hardy-Weinberg equilibrium and change genotype frequencies.

The effects ripple through evolution. Non-random mating can reinforce advantageous traits, create reproductive isolation, and even lead to speciation. It also impacts population structure, potentially forming distinct genetic clusters and reducing gene flow between subpopulations.

Non-Random Mating and Its Effects on Population Genetics

Forms of non-random mating

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• Non-random mating deviates from random mating expectations individuals choose mates based on specific traits or preferences
• Assortative mating involves individuals mating with partners sharing similar phenotypic traits (height, color)
  • Positive assortative mating like mates with like (tall people with tall people)
  • Negative assortative mating opposites attract (extroverts with introverts)
• Inbreeding occurs when closely related individuals mate (siblings, cousins)
• Sexual selection involves mate choice based on specific traits that increase reproductive success (peacock tail feathers)

Effects on population genetics

• Genotype frequency changes increase homozygous genotypes decrease heterozygous genotypes
• Allele frequencies remain unchanged directly but may shift indirectly through selection pressures
• Hardy-Weinberg equilibrium disrupted as non-random mating violates key assumption
• Linkage disequilibrium increases association between alleles at different loci
• Genetic drift enhanced in small populations with non-random mating
• Offspring more likely to inherit parental traits increased expression of recessive alleles
• Potential increase in extreme phenotypes reduction in intermediate phenotypes

Evolutionary impact of assortative mating

• Reinforcement of advantageous traits in specific environments (thick fur in cold climates)
• Reproductive isolation creates potential barrier to gene flow between populations
• Possible accumulation of deleterious alleles in homozygous state (genetic disorders)
• Sympatric speciation divergence without geographic isolation (apple maggot flies)
• Reinforcement strengthening of reproductive barriers (pollen incompatibility in plants)
• Adaptive radiation diversification of species in response to new ecological opportunities (Darwin's finches)

Consequences for population structure

• Population subdivision forms distinct genetic clusters within a population
• Gene flow reduction decreases genetic exchange between subpopulations
• Genetic divergence accumulates differences between subpopulations over time
• Reproductive barriers develop pre-zygotic and post-zygotic isolation mechanisms
• Genetic bottlenecks in small isolated populations reduce genetic diversity
• Management strategies for maintaining genetic diversity crucial for conservation efforts (captive breeding programs)