3.9—Loci and gene linkage

A locus is the position of a gene on a chromosome. Different alleles occupy the same locus, but genes at different loci may be linked if they lie on the same chromosome and tend to travel together through meiosis.

Linked genes do not assort independently in the simple way that genes on different chromosomes do. Crossing over can separate linked alleles, so offspring may show parental combinations more often than recombinant combinations.

If two genes are close on one autosome, gametes usually retain the parental allele combinations; a crossover between their loci creates a less frequent recombinant combination.

Linkage is about physical chromosome location, not about two traits looking similar. Sex-linked genes require the X/Y context, while autosomal linkage concerns non-sex chromosomes.