Structure of the goat ψβy β-globin pseudogene : Analysis of goat pseudogene evolutionary patterns

Abstract

The 12-member β-globin gene locus of the goat contains three beta(adult)-type pseudogenes, one in each of three four-gene subsets of the locus. We have determined the complete nucleotide sequence of ψβ y, the pseudogene present in the most downstream four-gene subset, which also contains the functional fetal gene, β F, ψβ y contains, throughout its length, numerous incapacitating mutations in common with the previously sequenced goat ψβ x and ψβ z pseudogenes consistent with the model that all were descended from a common pseudogene ancestor which became defective prior to the expansion of the β-globin locus in the goat lineage. Evolutionary analysis of the ψβ y sequence in comparison to ψβ x and ψβ z provides evidence that nucleotide substitutions were fixed in a random manner within these pseudogenes with respect to polarity, coding versus non-coding regions, and replacement sites versus silent sites. However, substitutions appear to have accumulated asymmetrically between different pseudogenes in a manner that provides evidence for partial gene conversion. Moreover, the presence of deletions in goat ψβ y, which are also observed in the cow pseudogene ψ 2, but not in the cow ψ 1 pseudogene, indicate that goat ψβ y and cow ψ 2 are orthologous but cow ψ 1 actually arose prior to the goat/cow divergence. The authentic goat orthologue to cow ψ 1 temporarily existed in the goat lineage but was deleted, probably prior to the divergence of goats and sheep.