Genetics and anthropology of Caucasian nations and the problem of "caucasoids" origin

Anthropological investigations have shown that representatives of European and mongoloid races lived in the river basin of Aragvi from late Stone Age. These data confirm a viewpoint of academician V.P. Alekssev (1974) that population of the Caucasus was compound in race terms from the ancient times. Situation of the Caucasian peoples on the dendrogrammes built corresponds in general to the data of national anthropologists. Clusterization of other europeoid ethnic groups also corresponds in general to the anthropological and historical data and confirms hypothesis which we have set up earlier about differentiation of europeoids, north mongoloids and amerinds of the same population which lived in Asia in palaeolith.     

On the equality of origin and fixation times in genetics

For any sexually reproducing entity (e.g. asexual organism, mitochondrion or gene), the fixation time is the number of generations in the future before all entities are descended from a single one in the present. The origin time is the number of generations in the past when a single entity was ancestral to all entities in the present. It is proved that, over a sufficiently long time, the means and distributions of the fixation and origin times are identical. The proof holds even if population size varies, selection is acting, or conditions change with time.     

Speciation genetics: epistasis, conflict and the origin of species

Evolutionary biologists have long recognized that the sterility and inviability of species hybrids must involve incompatible epistatic interactions between two (or more) genes. The first pair of such hybrid incompatibility genes has now been identified.     

Allopolyploid origin and population genetics of the rare orchid Spiranthes diluvialis

The process of becoming and the attributes of being polyploid play a major role in the development and maintenance of genetic variation in allopolyploid species. A genetic survey employing protein electrophoresis on 12 populations of S. diluvialis, as well as on populations of eight congeneric species, was conducted to assess the putative allopolyploid origin of S. diluvialis and to determine the genetic variability within and among populations. Genetic identity values indicated S. diluvialis was more similar to S. magnicamporum (0.619) and S. romanzoffiana (0.727) than to any of the other congeneric species assayed. Similar to most allopolyploids, S. diluvialis showed high levels of fixed, or nearly fixed, heterozygosity and a high percentage of polymorphic loci (57.1-71.4%). The mean number of alleles per polymorphic locus in populations of S. diluvialis (2.6-3.3), however, was similar to mean values for both animal-pollinated, outcrossing, diploid species, and geographically restricted, diploid species (2.6 and 2.5, respectively). Genetic divergence among populations (mean Fst = 0.083) was low, leading to relatively high estimates of interpopulational gene flow (mean Nm = 5.41). Thus, each population harbors most of the genetic variability found within the species. The genetic variation observed within S. diluvialis supports the occurrence of at least two separate hybridization events giving rise to S. diluvialis.     

The population genetics of Trypanosoma brucei and the origin of human infectivity

The African trypanosome, Trypanosoma brucei, is a zoonotic parasite transmitted by tsetse flies. Two of the three subspecies, T. brucei gambiense and T.b. rhodesiense, cause sleeping sickness in humans whereas the third subspecies, T.b. brucei, is not infective to humans. We propose that the key to understanding genetic relationships within this species is the analysis of gene flow to determine the importance of genetic exchange within populations and the relatedness of populations. T.brucei parasites undergo genetic exchange when present in infections of mixed genotypes in tsetse flies in the laboratory, although this is not an obligatory process. Infections of mixed genotype are surprisingly common in field isolates from tsetse flies such that there is opportunity for genetic exchange to occur. Population genetic analyses, taking into account geographical and host species of origin, show that genetic exchange occurs sufficiently frequently in the field to be an important determinant of genetic diversity, except where particular clones have acquired the ability to infect humans. Thus, T. brucei populations have an 'epidemic' genetic structure, but the better-characterized human-infective populations have a 'clonal' structure. Remarkably, the ability to infect humans appears to have arisen on multiple occasions in different geographical locations in sub-Saharan Africa. Our data indicate that the classical subspecies terminology for T. brucei is genetically inappropriate. It is an implicit assumption in most infectious disease biology that when a zoonotic pathogen acquires the capability to infect humans, it does so once and then spreads through the human population from that single-source event. For at least one major pathogen in tropical medicine, T. brucei, this assumption is invalid.     

On the problem of the origin of Pogonophora

A number of embryological features of the Pogonophora suggest that they could not derive from the Polychaeta and are closely related to Deuterostomia. These are: (1) traces of spiral cleavage that sharply differ the from cleavage of polychaetes in the prospective value of blastomeres; (2) enterocoelic formation of mesoderm; (3) the larva most closely resembles Balanoglossus that has just completed metamorphosis; proto-, meso-, and metasoma of pogonophoran larva correspond (or are homologous) to the proboscis, collar, and trunk of Balanoglossus respectively; while the telosoma can be regarded as an organ appearing late in phylogenesis that serves to burrow into the bottom; (4) larvae of Siboglinum have a transitory mouth located, as it is the case in Enteropneusta, between proto-and mesosoma, very far from the posterior end, where there is closed blastopore; therefore, the former can be considered as a secondary mouth; (5) the asymmetrical development of the anterior pair of coeloms in Pogonophora, Echinodermata, and Amphioxus allows finding homologies between organs developing from these coeloms.     

The origin of homoiothermy--unsolved problem

The analysis of allometric dependence of energy expenditure on body mass among reptiles, birds and mammals has shown that standard metabolic rate of reptiles when they are warmed up to the temperature of homoiothermic animals is an order of magnitude lower than that of birds and mammals. Basal metabolism is originated as special feature historically related to the metabolism during active behavior, rather than thermal regulation. Facultative endothermy was not advantageous for large animals because of long time needed to warm up the body. The ancestors of birds and animals escaped negative consequences of van't-Hoff equation by choosing constant body temperature. Heat conductivity of reptile's covers is so great, that it cannot keep endogenous warm of resting animal at any temperature of the body. Reptile "dressed" in covers of bird or mammal would be able to keep warm under conditions of maximal aerobic muscular activity and body temperature similar to that of homoiothermic animals. The base of chemical thermoregulation in birds and mammals is a thermoregulatory muscle tonus which remains unknown. One can suppose that during evolution of birds and mammals the saltation-liked origin of endothermy "fixed" the level of metabolism typical for running reptile and transformed in into the basal metabolism. This event took place at the cell and tissue level. The absence of palaeontological evidences and intermediate forms among recent species does not allow easy understanding of homoiothermy origin.     

The population genetics of the origin and divergence of the Drosophila simulans complex species

The origins and divergence of Drosophila simulans and close relatives D. mauritiana and D. sechellia were examined using the patterns of DNA sequence variation found within and between species at 14 different genes. D. sechellia consistently revealed low levels of polymorphism, and genes from D. sechellia have accumulated mutations at a rate that is approximately 50% higher than the same genes from D. simulans. At synonymous sites, D. sechellia has experienced a significant excess of unpreferred codon substitutions. Together these observations suggest that D. sechellia has had a reduced effective population size for some time, and that it is accumulating slightly deleterious mutations as a result. D. simulans and D. mauritiana are both highly polymorphic and the two species share many polymorphisms, probably since the time of common ancestry. A simple isolation speciation model, with zero gene flow following incipient species separation, was fitted to both the simulans/mauritiana divergence and the simulans/sechellia divergence. In both cases the model fit the data quite well, and the analyses revealed little evidence of gene flow between the species. The exception is one gene copy at one locus in D. sechellia, which closely resembled other D. simulans sequences. The overall picture is of two allopatric speciation events that occurred quite near one another in time.     

Population genetics of the peoples of Iran I. Genetic polymorphisms of blood groups,serum proteins and red cell enzymes

Genetic polymorphisms of six blood groups and seven biochemical genetic markers were investigated in six Iranian populations (Turks, Kurds, Lurs, Zabolis, Baluchis and Zoroastrians). Eight of the genetic systems (ABO, MNSs, Kidd, C3, AP, AK, PGM1 and EsD) showed conclusive heterogeneity among these populations. Comparison of gene frequencies with the few available samples of Iranian populations demonstrated an intra-ethnic and extensive overall genetic diversity in the Iranian plateau. A gradient of C3*F gene was also discernible within the geographical region of Iran which may reflect the relics of the historical movements of different racial groups in this region. The present genetic variation may reflect the differences in the structure of these populations, the analysis of which is further attempted in the accompanying paper.