4 Chapter 4 – Linkage and Linkage Disequilibrium

In Chapter 4 we will look at something that, on the surface, challenges the notion of Hardy-Weinberg Equilibrium – linkage. Linkage messes up our perception of H-WE but, as I hope you see once we explore it, it doesn’t actually change allele frequencies. Instead, linkage changes how we see multi-loci genotypes expressed in a way that suggests allele and genotypic frequencies are being altered.

When loci are linked, they do not segregate independently. Mating is does not appear to be random with respect to the linked loci. Linkage refers to a broad concept and can be further broken down into sub-topics. Sex linkage where the locus of interest is located on one of the sex chromosomes and autosomal linkage where the two loci of interest occur on the same chromosome. It is outside the scope of this book, but the appearance autosomal linkage involving two loci on different chromosomes can also be created by selection.