Final answer:
Linkage disequilibrium involves non-random associations between alleles at different loci and is characterized by certain allele combinations occurring more or less frequently than expected in a population. It is influenced by genetic linkage and recombination frequency, affecting the expected frequency of recombinant offspring and being important in the study of genetic variation and evolution.
Step-by-step explanation:
Linkage disequilibrium refers to the non-random association of alleles at two or more loci, not necessarily on the same chromosome. It can be influenced by several factors including genetic linkage, recombination frequency, and evolutionary forces. When alleles are in linkage disequilibrium, the frequency of certain allele combinations in a population is higher or lower than expected based on their individual frequencies. Genetic linkage contributes to linkage disequilibrium when groups of genes that are close together on a chromosome are less likely to be separated by recombination, thus they are inherited together more often than not.
Sturtevant's work on genetic linkage maps reflects the calculation of distances between genes, where a recombination frequency of 0 indicates perfect linkage and 0.5 indicates no linkage, meaning that alleles on different chromosomes or very far apart on the same chromosome assort independently. However, as the recombination frequency approaches 0.50, it becomes difficult to determine whether genes are far apart on the same chromosome or on different chromosomes.
In practice, a recombination frequency of less than 50 percent indicates linkage, which affects the allele combinations seen in offspring. For instance, in a dihybrid cross, if two genes are linked, the expected frequency of recombinant offspring will be less than 50 percent. This combination of linked genes can result in observable phenotype patterns, aiding in the construction of genetic maps and providing insights into the processes that drive genetic variation and evolution.