Define linkage disequilibrium. What is the physical basis of linkage, and what causes linkage equilibrium? Explain how crossing over eliminates linkage disequilibrium.

Key Concepts

Linkage Disequilibrium

Linkage disequilibrium refers to the non-random association of alleles at different loci in a given population. When certain alleles are inherited together more often than would be expected by chance, it indicates that the loci are physically close on the same chromosome. This can affect genetic variation and the mapping of traits in populations.

Physical Basis of Linkage

The physical basis of linkage lies in the arrangement of genes on chromosomes. Genes that are located close to each other on the same chromosome tend to be inherited together during meiosis, due to the reduced likelihood of recombination events occurring between them. This proximity can lead to the phenomenon of linkage disequilibrium.

Crossing Over and Linkage Equilibrium

Crossing over is a process during meiosis where homologous chromosomes exchange segments, leading to new combinations of alleles. This recombination can break up the associations between alleles at linked loci, promoting linkage equilibrium, where allele combinations occur randomly. As a result, crossing over reduces linkage disequilibrium by increasing genetic diversity.