Final answer:
Linkage disequilibrium in random-mating populations arises when there are evolutionary forces like natural selection, genetic drift, or gene flow that change allele frequencies. The Hardy-Weinberg Equilibrium can be used to measure these changes, with its violation indicating active microevolution in the population.
Step-by-step explanation:
Selection on multilocus genotypes in random-mating populations leads to linkage disequilibrium when natural selection, genetic drift, gene flow, or non-random mating affect the allele frequencies in a population. This can occur when adaptive differences between individuals and populations affect certain loci, causing the frequency of alleles at these loci to deviate from expectations based on migration and genetic drift balances. Under such selective pressures, alleles that are physically linked to advantageous traits can increase in frequency together, leading to linkage disequilibrium.
Hardy-Weinberg Equilibrium and its Violation
The Hardy-Weinberg Equilibrium is a principle that provides the conditions under which allele and genotype frequencies remain constant in a population over time. Violations of this equilibrium, such as non-random mating, mutations, small population size, natural selection, and gene flow, lead to evolutionary changes in the population, or microevolution.