Evolutionary relationships of human populations on a global scale.

Using gene frequency data for 29 polymorphic loci (121 alleles), we conducted a phylogenetic analysis of 26 representative populations from around the world by using the neighbor-joining (NJ) method. We also conducted a separate analysis of 15 populations by using data for 33 polymorphic loci. These analyses have shown that the first major split of the phylogenetic tree separates Africans from non-Africans and that this split occurs with a 100% bootstrap probability. The second split separates Caucasian populations from all other non-African populations, and this split is also supported by bootstrap tests. The third major split occurs between Native American populations and the Greater Asians that include East Asians (mongoloids), Pacific Islanders, and Australopapuans (native Australians and Papua New Guineans), but Australopapuans are genetically quite different from the rest of the Greater Asians. The second and third levels of population splitting are quite different from those of the phylogenetic tree obtained by Cavalli-Sforza et al. (1988), where Caucasians, Northeast Asians, and Ameridians from the Northeurasian supercluster and the rest of non-Africans form the Southeast Asian supercluster. One of the major factors that caused the difference between the two trees is that Cavalli-Sforza et al. used unweighted pair-group method with arithmetic mean (UPGMA) in phylogenetic inference, whereas we used the NJ method in which evolutionary rate is allowed to vary among different populations. Bootstrap tests have shown that the UPGMA tree receives poor statistical support whereas the NJ tree is well supported. Implications that the phylogenetic tree obtained has on the current controversy over the out-of-Africa and the multiregional theories of human origins are discussed.

Genetic relationships of the populations in eastern India.

The genetic relationships for four sets of populations in eastern India have been studied by using gene frequency data available in the literature. The Caucasoid populations in Assam and West Bengal are genetically close but different from the Mongoloid populations in the neighbourhood. The genetic distance analysis shows that the Mongoloid populations in Assam and West Bengal cluster according to their states of residence, indicating a correlation between genetic and geographical distances.

Genetic relationships between Indians and their neighboring populations.

Using gene frequency data for 18 protein and blood group loci, we studied the genetic relationships of four Indian subcontinent populations (peoples from Punjab, Gujarati, Andhra Pradesh, and Bangladesh) with their neighboring populations (Iranians, Afghans, Sinhalese in Sri Lanka, Nepalese, Bhutanese, Malays, Bataks in northern Sumatra, and Chinese). The results obtained indicate that the four Indian subcontinent populations and the Sinhalese are genetically closer to Iranians and Afghans (Caucasoid) than to the other neighboring Mongoloid populations. Genetic distance analysis shows a clear-cut dichotomy between the Caucasoid and Mongoloid populations.

Genetic relationship between Indian tribes and Australian Aboriginals.

Using gene frequency data of ten blood group and protein loci (A1A2BO, MNSs, Rh, P, Lu, Fy, Hp, Tf, Hb beta and Gm) the genetic relationships of three tribes, namely, the Toda, Irula, Kurumba in south India and one tribe, namely, the Veddah in Sri Lanka with the Aboriginals in Malay, New Guinea and Australia were studied by genetic distance analysis. The tribes in south India and Sri Lanka are genetically closer to one another than to the Aboriginals in southeast Asia and Oceania. Despite their morphological similarity there is no genetic evidence to suggest that the Indian tribes and Australian Aboriginals are biologically related.

Red cell enzyme polymorphism: gene differentiation in three populations of Maharashtra, India.

Blood samples of 1,266 individuals were collected from three caste populations; Nava Budha (Mahar), Maratha, and a mixed group of Scheduled castes from each of three districts of Maharashtra, Nagpur, Akola, and Thane. The samples were tested for 12 enzyme systems, viz., AcPh, AK, CA-I, CA-II, Est-D, LDH, MDH, Oxidase, PGM-1, PGM-2, 6-PGD, and PHI. The gene frequencies of these loci are within the ranges observed among the Indian populations so far studied. The total differences in gene frequencies for each polymorphic locus was partitioned into three components, i.e., the differences between caste populations, the differences between regions, and the differences due to interaction between caste populations and regions. The results show that besides caste variation for two loci, Est-D and PGM-1, the gene frequencies for AK, Est-D, and G-6PD loci have different geographical distributions.

Is there a pattern of gene differentiation in the Indian populations.

Indian populations divided into a number of endogamous groups consisting of different castes, languages, religions, and tribes provide unique opportunities for examining the extent and nature of genetic differentiation at a microevolutionary stage. The genetic relationships between some of these Indian population groups have been examined using electrophoretic data from several biochemical loci in a gene diversity analysis. Does this type of analysis provide any insight into what causes such gene differentiation? What patterns of genetic variation emerge from these empirical findings? Answers are sought by relating the observed heterozygosity, genetic distance, and allied statistics to a mutation-drift hypothesis. The statistics used are: (1) interlocus mean and variance of heterozygosity, (2) mean and variance of genetic distance, and (3) correlation of heterozygosity and gene identity. The observed relationships between these sets of statistics agree well with the ones predicted by the hypothesis that different alleles at protein loci are selectively equivalent and gene frequency change occurs predominantly due to genetic drift.

Mutation rates from rare variants of proteins in Indian tribes.

Recent attempts to estimate mutation rates in man have resulted in some theoretical developments. Recently, Nei (1977) provided a new formula for estimating mutation rates from electrophoretically detected rare protein variants. His formula is applied here to estimated mutation rates from such variants among the Kadars of Kerala and five tribes of Andhra Pradesh in India. The estimates seem to differ from Nei's estimate on South American Indians by an order of magnitude, although the standard errors associated with such estimates are rather large.

Genetic distance between the American Indians and the three major races of man.

The genetic distances between the American Indians and the three major races of man, Caucasoids, Negroids and Mongoloids, were determined by using gene frequency data on 14 blood group and 12 protein loci. The results support the general view that the ancestry of the American Indian is predominantly Mongoloid. Using 30,000 years as the separation time between the American Indian and Mongoloid, the divergence time between the three major races of man was estimated to be 33,000-92,000 years.

Gene diversity in Indian populations.

Gene frequency data of ten protein and enzyme loci in seven populations of India were collected from the literature. The gene differentiation among seven populations relative to total population was only 0.6%, indicating that the genic variation between populations was small compared to that within them. Using 29 common protein loci, the genetic distances between Indians and three major races of man, Caucasoids, Mongoloids, and Negroids were also determined. Indians are closer to Mongoloids than to Caucasoids or Negroids as indicated by the phylogenetic tree.

Gene differentiation in three tribes of American Indians.

The amount of gene differentiation in the subdivided populations of three American Indian tribes, the Papago, Makiritare and Yanomama were studied and found to vary from 2 to 7%. These results indicate that only small fractions of the total gene differences are attributable to between subpopulations and the remaining 93-98% to within subpopulations.

Genetic distance and gene diversity among linguistically different tribes of Mexican Indians.

Using gene frequency data for 14 genetic loci, genetic distances between 13 tribes of Mexican Indians belonging to 12 language groups were determined and a dendrogram was constructed. The genetic distance between tribes is correlated more with geographic proximity than with language affinity. The gene diversity (heterozygosity) of the total population was decomposed into the three components, i.e., the gene diversity between three main linguistic groups, the gene diversity between tribes within the main linguistic groups and the gene diversity within tribes. About 95% of the total gene diversity exists within tribes, the intergroup and intertribe components being only about 5%.

Sampling variances of heterozygosity and genetic distance.

Mathematical formulae for the sampling variances of average heterozygosity and Nei's genetic distance are developed. These sampling variances are decomposed into their two components, i.e. the inter-locus and intra-locus variances. The relationship between the number of loci and the number of individuals per locus to be examined for estimating average heterozygosity and genetic distance is also discussed. The utility of the inter-locus variance of heterozygosity for studying the mechanism of maintenance of genetic variability in populations is indicated.

Probability of fixation and mean fixation time of an overdominant mutation.

The probability of fixation of an overdominant mutation in a finite population depends on the equilibrium gene frequency in an infinite population (m) and the product (A) of population size and selection intensity. If m < 0.5 (disadvantageous overdominant genes), the probability is generally much lower than that of neutral genes; but if m is close to 0.5 and A is relatively small, it becomes higher. If m > 0.5 (advantageous overdominant genes), the probability is largely determined by the fitness of heterozygotes rather than that of mutant homozygotes. Thus, overdominance enhances the probability of fixation of advantageous mutations. The average number of generations until fixation of an overdominant mutation also depends on m and A. This average time is long when m is close to 0.5 but short when m is close to 0 or 1. This dependence on m and A is similar to that of Robertson's retardation factor.

Gene differences between Caucasian, Negro, and Japanese populations.

The numbers of gene (codon) differences per locus between two randomly chosen genomes within and between Caucasian, Negro, and Japanese populations have been estimated from gene frequency data for protein loci. The estimated number of gene differences between individuals from different populations is only slightly greater than the number between individuals from the same population.