Evolution of nuclear gene families in primates. Copy-number variation in the argininosuccinate synthetase (ASS) pseudogene family and the anonymous DNA sequence, D1S1.

Abstract

Changes in the copy number of nuclear genes provide the raw material for the creation of new gene functions. To better understand the mechanisms for such events, and their physiologic and evolutionary consequences, it is valuable to study a well characterized and closely related group of species such as primates. Fortuitously, most of the powerful molecular techniques and DNA probes developed for research in humans are equally applicable to non-human primates. We review what is known of copy number variation in primates and describe two informative DNA probes: pAS-1, a cDNA probe to the human urea cycle enzyme argininosuccinate synthetase (ASS), and an anonymous DNA probe, D1S1. In addition to the ASS structural locus on human chromosome 9, pAS-1 detects at least 14 dispersed, processed pseudogenes in humans. The number of pseudogene copies appears to be approximately the same in humans, chimpanzees, gorillas, orangutans and baboons; less in marmosets; and least in some rodents. Chimpanzees and gorillas appear to have all of the human pseudogenes though an Xp copy may be missing from gorillas. The Y pseudogene is apparently absent from orangutans and baboons, and, finally, a comparison of humans and chimpanzees revealed that the number of nucleotide substitutions in the Y chromosome pseudogenes is approximately 1 per 100. D1S1 maps to human chromosome 3 but also detects a high homology copy on chromosome 1. Chimpanzees, gorillas and orangutans all appear to have only the chromosome 3 homolog suggesting that this is the ancestral sequence and that the duplication occurred after separation of humans and the great apes. Both the ASS pseudogene family and the D1S1 system provide valuable information on the evolution of nuclear gene families in primates.