The isolation-by-distance model predicts that genetic similarity between populations will decrease exponentially as the geographic distance between them increases, because of the limiting effect of geographic distance on rates of gene flow. Many studies of human populations have applied the isolation-by-distance model to genetic variation between local populations in a limited geographic area, but few have done so on a global level, and these few used different models and analytical methods. I assess genetic variation between human populations across the world using data on red blood cell polymorphisms, microsatellite DNA markers, and craniometric traits. The isolation-by-distance model provides an excellent fit to average levels of genetic similarity within geographic distance classes for all three data sets, and the rate of distance decay is the same in all three. These results suggest that a common pattern of global gene flow mediated by geographic distance is detectable in diverse genetic and morphological data. An alternative explanation is that the correspondence between genetic similarity and geographic distance reflects the history of dispersal of the human species out of Africa.
isolation by distance, gene flow, red blood cell polymorphisms, microsatellite DNA, craniometrics.
Vandeberg, John L.
Upadhayay, Ram Prasad.
Rai, Dev Raj.
The soil-transmitted helminths are the most common helminthic infections, affecting about one-fourth of the world's population. There is a significant genetic component to susceptibility to infection with these organisms. Substantial changes in plasma cytokine levels are associated with helminthic infections, and there may be significant genetic components to this cytokine variation. Six plasma cytokine levels were assessed for 367 members of a single pedigree from the Jirel population of eastern Nepal. This population experiences moderate rates of infection with geohelminths. Sex, age, helminthic infection, infection with Giardia, and presence of a household latrine were considered as covariates in all analyses of the cytokine data. The analyses of the single Jirel pedigree revealed significant heritabilities for IFN-γ (h2 = 0.654 ± 0.096), TNF-α (h2 = 0.458 ± 0.101), IL-2 (h2 = 0.583 ± 0.101), IL-4 (h2-0.700 ± 0.095), IL-5 (h2 = 0.676 ± 0.087), and IL-10 (h2 = 0.597 ± 0.093). The ratios of IL-4 to IFN-γ and of IL-10 to IFN-γ were used as indicators of the degree of type 2 bias in immunological response; analyses of these variables indicated that approximately 40-60% of the variation (h2 = 0.400-0.577) in these derived measures of relative type 2/type 1 response is due to genetic factors.
Human population genetics -- Comoros -- Grande Comore.
Racially mixed people -- Comoros -- Grande Comore.
The Comorian population is historically considered a blend of influences from African Bantus, Arabs, and possibly Austronesians. In this study we present the first genetic data on the current Comorian population. Serologic analysis of the six major blood group systems (ABO, RH, KEL, FY, JK, and MNS) was performed on 164 individuals from Grande Comore Island (Njazidja). In addition, Duffy genotypes were determined by polymerase chain reaction using allele-specific primers. Our findings establish a high frequency of the Fy(a– b–) phenotype (86%), presenting the same genetic background as in sub-Saharan Africa. Analysis of genetic frequencies, distances, and admixture with other populations indicates that African Bantus made the main contribution to the gene pool (73.2% ± 15.5%). The Arab contribution from the Arabian peninsula was smaller (24.2% ± 7%) and the Indonesian contribution was minor (2.6% ± 9%). The major Bantu contribution was commensurate with the Bantu cultural influence. The contribution from the Arabian peninsula seemed in relation to its permeating religious and linguistic influence. As with the language, the Indonesian contribution to the Comorian gene pool was small. These results are in agreement with historical, sociological, and linguistic data.
Human population genetics -- Argentina -- La Plata.
In this study we analyzed a sample of the urban population of La Plata, Argentina, using 17 mtDNA haplogroups, the DYS199 Y-chromosome polymorphism, and 5 autosomal population-associated alleles (PAAs). The contribution of native American maternal lineages to the population of La Plata was estimated as 45.6%, whereas the paternal contribution was much lower (10.6%), clearly indicating directional mating. Regarding autosomal evidence of admixture, the relative European, native American, and West African genetic contributions to the gene pool of La Plata were estimated to be 67.55% (±2.7), 25.9% (±4.3), and 6.5% (±6.4), respectively. When admixture was calculated at the individual level, we found a low correlation between the ancestral contribution estimated with uniparental lineages and autosomal markers. Most of the individuals from La Plata with a native American mtDNA haplogroup or the DYS199*T native American allele show a genetic contribution at the autosomal level that can be traced primarily to Europe. The results of this study emphasize the need to use both uniparentally and biparentally inherited genetic markers to understand the history of admixed populations.
The GM polymorphism of human immunoglobulins is analyzed in three Berber populations of southern Tunisia and compared to other GM data. Genetic diversity among Tunisian populations is higher than that among Europeans but does not exhibit any significant geographic or linguistic structure. This result suggests a complex pattern of genetic differentiation.
arabs, berbers, GM, human genetic diversity, immunoglobulins, North Africa, Tunisia.
Langstieh, B. T.
Reddy, B. Mohan.
The autosomal AmpFLSTR markers validated and widely used for forensic applications are used in this study to examine the extent of diversity and genetic relationships among nine Meghalaya populations. Altogether, 932 chromosomes from 9 populations were analyzed using 9 tetrameric AmpFLSTR loci. The included populations were all seven subtribes of the Austro-Asiatic Mon-Khmer-speaking Khasi and the neighboring Tibeto-Burman Garo. The Lyngngam, which are linguistically closer to the Khasi but are culturally intermediate between the Khasi and the Garo, are also included in the study. Although most of the microsatellite loci are highly polymorphic in each of these populations, the allele distributions are fairly uniform across the Meghalaya populations, suggesting relative homogeneity among them. Concurrent with this, the coefficient of gene differentiation (GST) is observed to be low (0.026 ± 0.002). This is naturally reflected in the lack of clear differentiation and clustering pattern of the Meghalaya tribes based on either geographic proximity or the historical or current affiliations of these tribes. Analysis of molecular variance (AMOVA) suggests no significant population structure. The structure analysis further suggests that, barring War-Khasi and Pnar, no other population shows any semblance of genetic identity. Even the position of the linguistically distinct Garo is not portrayed as separate from the Khasi. However, when comparable data from other Indian, Southeast Asian, and other continental populations were analyzed, the Meghalaya populations formed a compact cluster clearly separated from other populations, suggesting genetic identity of the Meghalaya populations as a whole. These results are concurrent with the hypothesis of a common and recent origin of these Meghalaya populations, whose genetic differentiation is overwhelmed by the homogenizing effect of continuous gene flow.
Heller, A. H.
Salzano, Francisco M.
Arnett, Frank C. (Frank Couchman), 1942-
Hutz, M. H.
Carnese, F. R.
Goicoechea, A. S.
Freitas, L. B.
Bonatto, S. L.
Human population genetics -- Russia (Federation) -- Siberia.
One-hundred three individuals from two Mongolian, two Siberian, and ten native American populations were studied in relation to a 340-bp sequence from an Alu insertion located in the 3' untranslated region of the LDLR gene. Seven haplotypes have been determined, and haplotype B1 was the most common, accounting for about half the sequences found. In general, diversity values are quite high, about 2.5 times higher than those found in other autosomal Alu sequences. Almost all (93%) of the variability occurs at the intrapopulation level, but the greatest among-group differentiation (6-8%) was found when we grouped in a single population all Native Americans plus Siberian Eskimos and Chukchi and compared them with Mongolians. This result is compatible with earlier mtDNA and Y-chromosome suggestions of a single origin for the first colonizers of the American continent. With this nuclear locus it was not possible to broadly distinguish between Central and South American natives. No evidence of selection or marked demographic changes was obtained with these data.
Teenagers -- Health and hygiene -- Mexico -- Mexico City.
Previous studies in the Mexican population have failed to show an effect of apolipoprotein E (APOE) polymorphism on the lipid profile. The purpose of the present study was to determine the frequencies of APOE phenotypes, and their influence on lipid and apolipoprotein levels in a random sample of Mexican adolescents living in Mexico City. APOE polymorphism, fasting insulin levels, lipid levels, and apolipoprotein levels were determined in 420 adolescents. We found a high frequency of APOE*3 subjects (89.5%) and a low frequency of APOE*2 (3.0%) and APOE*4 (7.5%) subjects. The APOE*4 subjects (including APOE 4,3 and APOE 4,4) showed the highest concentrations of total cholesterol, low-density lipoprotein cholesterol, and apoB and the lowest high-density lipoprotein cholesterol levels, whereas carriers of the APOE*2 allele (APOE 3,2 and APOE 2,2) had the lowest values for total and low-density lipoprotein cholesterol and the highest concentrations of high-density lipoprotein cholesterol. No significant differences in triglyceride and insulin levels among subjects with different APOE polymorphisms were observed. Unlike previous studies in the Mexican population, our results show that lipid and lipoprotein levels are under the influence of APOE polymorphism. As in whites, APOE*4 may be a cardiovascular risk factor in the Mexican population.
We investigate whether a varying distribution of the APOE genotype could help explain regional differences in ischemic heart disease (IHD) mortality in Spain. APOE genotypes were examined by PCR in 1,274 randomly selected healthy children from four Spanish regions with different adult IHD mortality rates (northwest and central Spain with low rates and southeast and southern Spain with high rates). In the population as a whole the prevalence of the higher risk APOE*3/*4 genotype is 16.8% and the prevalence of the APOE*4 allele is 10.1%. In northwest Spain the frequencies of the APOE*3/*4 genotype (12.9%) and of the APOE*4 allele (8.3%) are smaller than in the other regions. The southeast region shows statistically higher frequencies of the APOE*3/*4 genotype (22.5%) and of the APOE*4 allele (13.2%) than in the other regions or in the group as a whole. We can conclude that Spain is not homogeneous in terms of APOE genotype distribution. Although the prevalence of the APOE*4 allele is generally low, there are areas with higher prevalence of the APOE*4 allele and a higher incidence of adult IHD mortality. This allows us to conclude that in Spain this genetic determinant can be associated with IHD mortality in relatively isolated populations.
In all human populations mean life span of women generally exceeds that of men, but the extent of this sexual dimorphism varies across different regions of the world. Our purpose here is to study, using global demographic and environmental data, the general tendency of this variation and local deviations from it. We used data on male and female life history traits and environmental conditions for 227 countries and autonomous territories; for each country or territory the life-span dimorphism was defined as the difference between mean life spans of women and men. The general tendency is an increase of life-span dimorphism with increasing average male-female life span; this tendency can be explained using a demographic model based on the Makeham-Gompertz equation. Roughly, the life-span dimorphism increases with the average life span because of an increase in the duration of expressing sex- and age-dependent mortality described by the second (exponential) term of the Makeham-Gompertz equation. Thus we investigated the differences in male and female environmental mortality described by the first term of the Makeham-Gompertz equation fitted to the data. The general pattern that resulted was an increase in male mortality at the highest and lowest latitudes. One plausible explanation is that specific factors tied to extreme latitudes influence males more strongly than females. In particular, alcohol consumption increases with increasing latitude and, on the contrary, infection pressures increase with decreasing latitude. This finding agrees with other observations, such as an increase in male mortality excess in Europe and Christian countries and an increase in female mortality excess in Asia and Muslim countries. An increase in the excess of female mortality may also be due to increased maternal mortality caused by an increase in fertility. However, this relation is not linear: In regions with the highest fertility (e.g., in Africa) the excess of female mortality is smaller than in regions with relatively lower fertility (e.g., in Asia). A possible explanation of this phenomenon is an evolutionary adaptation of women to the pressures of extremely high fertility by means of some reduction of their maternal mortality.
sexual dimorphism, life span, mortality rate.
Carvalhaes, Fernanda Andreza de Pinho Lott.
Cardoso, Greice Lemos.
Hamoy, Igor Guerreiro.
Liu, Yan Tat.
Guerreiro, João Farias.
HIV infections -- Amazon River Region -- Genetic aspects.
Human population genetics -- Amazon River Region.
HIV infections -- Brazil -- Genetic aspects.
Human population genetics -- Brazil.
The frequency distribution of the CCR5-Δ32, CCR2-64I, and SDF1-3'A alleles was studied in the urban population of Belém and in Afro-Brazilians, Amerindians, and Japanese immigrants in the state of Pará, Brazil. The results suggest that Amerindians may be genetically more susceptible to HIV-1 infection and disease progression than the other human groups studied.