CONSERVATION OF HUMAN-CHROMOSOME-13 POLYMORPHIC MICROSATELLITE (CA)(N) REPEATS IN CHIMPANZEES

Tandemly repeated (dC-dA)(n).(dG-dT)(n) sequences occur abundantly and are found in most eukaryotic genomes. To investigate the level of con servation of these repeat sequences in nonhuman primates, we have anal yzed seven human chromosome 13 dinucleotide (CA)(n) repeat loci in chi mpanzees by DNA amplification using primers designed for analysis of h uman loci. Comparable levels of polymorphism at these loci in the two species, revealed by the number of alleles, heterozygosity, and allele sizes, suggest that the (CA)(n) repeat arrays and their genomic locat ions are highly conserved. Even though the proportion of shared allele s between the two species varies enormously and the modal alleles are not the same, allelic lengths at each locus in the chimpanzees are det ected within the bounds of the allele size range observed in humans. A similar observation has been noted in a limited number of gorillas an d orangutans. Using a new measure of genetic distance that takes into account the size of alleles, we have compared the genetic distance bet ween humans and chimpanzees. The genetic distance between these two sp ecies was found to be ninefold smaller than expected assuming there is no selection or mutational bias toward retention of (CA)(n) repeat ar rays. These findings suggest a functional significance for these micro satellite loci. (C) 1994 Academic Press, Inc.