Final answer:
In the two-locus model, the loci mustn't be linked, meaning they are on separate chromosomes, for the Hardy-Weinberg conditions to be true.
Step-by-step explanation:
The Hardy-Weinberg equilibrium is a principle in population genetics that describes the stability of allele frequencies in a population over generations when certain conditions are met. In the context of a two-locus model, the key condition for Hardy-Weinberg equilibrium is that the loci must be unlinked.
Linkage refers to the tendency of genes located on the same chromosome to be inherited together, violating the assumption of independent assortment. If loci are linked, their alleles will not segregate independently during gamete formation, and the equilibrium conditions will not hold. The degree of linkage between loci can be quantified using a recombination fraction. A recombination fraction of 0 indicates complete linkage, while 0.5 signifies independent assortment.
In the two-locus model, maintaining Hardy-Weinberg equilibrium requires that the loci are on different chromosomes or are so far apart on the same chromosome that they assort independently during meiosis. This ensures that the alleles at one locus segregate independently of the alleles at the other locus, preserving the equilibrium conditions. Thus, understanding and accounting for linkage between loci are critical considerations when applying the Hardy-Weinberg equilibrium in a two-locus genetic model.