Evolution of modern humans: evidence from nuclear DNA polymorphisms.

Previously we have described studies of the evolution of modern humans based upon data for classical genetic markers and for nuclear DNA polymorphisms. Such polymorphisms provide a different point of view regarding human evolution than do mitochondrial DNA sequences. Here we compare revised dates for major migrations of anatomically modern humans, estimated from archaeological data, with separations suggested by a genetic tree constructed from classical marker allele frequencies. Analyses of DNA polymorphisms have now been extended and compared with those of classical markers; genetic trees continue to support the hypothesis of an initial African and non-African divergence for modern humans. We have also begun testing non-human primates for a set of human DNA polymorphisms. For most polymorphisms tested so far, humans share a single allele with other primates; such shared alleles are likely to be ancestral. Populations living in humid tropical environments have significantly higher frequencies of ancestral alleles than do other populations, supporting the hypothesis that natural selection acts to maintain high frequencies of particular alleles in some environments.     

Bacillus subtilis 168 mutants resistant to arginine hydroxamate in the presence of ornithine or citrulline

Mutations in Bacillus subtilis 168 have been isolated that confer resistance to arginine hydroxamate in the presence, but not absence, of ornithine. Seven such Ahor mutants have been studied in detail. In common with certain classes of Ahr mutant (resistant to arginine hydroxamate in the absence of arginine precursors) described previously, these Ahor mutants showed little or no inducibility of enzymes of arginine catabolism. Mutants that showed no inducibility were unable to utilize arginine or ornithine as sole nitrogen source. The only biosynthetic enzyme to show any consistent differences in activity from the parent was ornithine carbamoyltransferase, whose level was slightly elevated in cells grown in the presence of ornithine or citrulline. PBS1 transduction crosses showed that two of the ahor mutations map at the ahrA locus, while a third (unique in its resistance to arginine hydroxamate in the presence of citrulline) mapped at a hitherto undescribed locus closely linked to metC, designated ahrD.     

Sequence variation at the major histocompatibility complex locus DQ beta in beluga whales (Delphinapterus leucas) [published erratum appears in Mol Biol Evol 1995 Nov;12(6):1174]

Genetic variation at the Major Histocompatibility Complex locus DQ beta was analyzed in 233 beluga whales (Delphinapterus leucas) from seven populations: St. Lawrence Estuary, eastern Beaufort Sea, eastern Chukchi Sea, western Hudson Bay, eastern Hudson Bay, southeastern Baffin Island, and High Arctic and in 12 narwhals (Monodon monoceros) sympatric with the High Arctic beluga population. Variation was assessed by amplification of the exon coding for the peptide binding region via the polymerase chain reaction, followed by either cloning and DNA sequencing or single-stranded conformation polymorphism analysis. Five alleles were found across the beluga populations and one in the narwhal. Pairwise comparisons of these alleles showed a 5:1 ratio of nonsynonymous to synonymous substitutions per site leading to eight amino acid differences, five of which were nonconservative substitutions, centered around positions previously shown to be important for peptide binding. Although the amount of allelic variation is low when compared with terrestrial mammals, the nature of the substitutions in the peptide binding sites indicates an important role for the DQ beta locus in the cellular immune response of beluga whales. Comparisons of allele frequencies among populations show the High Arctic population to be different (P < or = .005) from the other beluga populations surveyed. In these other populations an allele, Dele-DQ beta*0101-2, was found in 98% of the animals, while in the High Arctic it was found in only 52% of the animals. Two other alleles were found at high frequencies in the High Arctic population, one being very similar to the single allele found in narwhal.