Variation in the Number of a-Globin Loci in Sheep’

Southern blot analysis was used to compare sheep and goat restriction-endonuclease maps of the DNA region containing the c@obin genes. The identical digestion patterns observed in both species with three endonucleases (BarnHI, BstEII, and PstI) show that in sheep a single chromosome normally bears two nonallelic CXglobin genes positioned at the same distance ai in goat. Variant digestion patterns with enzymes that cleave outside (BamHI and HindIII) and within (EcoRI) the a-globin loci allowed us to infer that chromosomes with different numbers of a-globin loci are also present in sheep. In particular, in the 60 sheep considered, four individuals were heterozygous (aa/aaa) and one was homozygous (aacz/aaa) for chromosomes with three loci and one individual was heterozygous for a chromosome with four loci (cm/cmaa). This variation in the number of copies of (rglobin loci can be explained by means of unequal crossovers.