Figure 3.5: Schematic illustration of gene loci on a pair of chromosomes Successive genes are depicted here as beads on a string. This pair of chromosomes is homozygous at loci 1, 3, and 5 (the paired genes there are identical to each other) and heterozygous at loci 2 and 4 (the paired genes there are not identical to each other). Nonidentical genes that can occupy the same locus on a pair of chromosomes are referred to as alleles of each other. Thus the two genes at locus 2 are alleles, as are the two at locus 4.