Skin colorimetry in Belize. I. Conversion formulae

Comparisons between skin colorimetry reports have been hampered by the common use of two different types of portable reflectometers, which sample reflectances at different wavelengths. In an attempt to provide direct comparability between the two machines, multiple linear regression equations were derived from reflectance spectrophotometry readings on 308 Black Caribs and 175 Creoles in Belize, Central America, using both machines. Cross validation tests show the coefficients presented are applicable to independent data sets and generally applicable to other heavily pigmented populations. Comparisons with previously published conversion formulae, which were from very small samples using simple linear regression, show a definite improvement in predictive accuracy when using multiple regression equations based on a large sample.     

Admixture estimation using skin reflectance data

Several different methods are suggested for the estimation of admixture proportions in hybrid populations based on skin reflectance data. These methods are applied to hybrid populations of known ancestry and yield results generally quite similar to those expected based on a simple genetic model. Results indicate the usefulness of these methods in hybridization studies and in the development and refinement of models of the genetics of skin color.     

Skin colorimetry in Belize. II. Inter- and intra-population variation

Skin colorimetry readings taken in Belize, Central America (formerly British Honduras) with the two most commonly used portable reflectometers reveal significant differences in mean reflectance between Garifuna (Black Caribs) and Creoles, and between Garifuna in two settlements. These differences are related to variation in African, Indian, and European admixture, as estimated from serological markers. Sex differences are not evident in univariate comparisons, but females are significantly lighter than males in multivariate analyses of variance. Polynomial age trends exist in some groups for certain variables, but account for a very small amount of the variation in skin color within these groups.     

Social class,admixture, and skin color variation in Mexican-Americans and Anglo-Americans living in San Antonio,Texas

Social class may act in different ways as a barrier to gene flow in urban populations, depending on ethnicity. We test the hypothesis that biological variation is affected by social class subdivision using skin reflectance data collected for 393 Anglo-American and 930 Mexican-American adults in the major urban population of San Antonio, Texas. Two socioeconomic groups were sampled for the Anglo-American population: a middle-income transitional group and a high-income suburban group. In addition, we sampled a third socioeconomic group for Mexican-Americans: a low income barrio. Sex and age effects on skin color are minimal. Social class has no effect on skin color variation for Anglo-Americans, whereas there is a highly significant effect on social class subdivision for Mexican-Americans. Admixture estimates were derived from skin reflectance data and show that the proportion of native American ancestry decreases as social class increases.     

Cherokee admixture and its estimation by the gene identity method: A critique

A previous application to a Cherokee hybrid population of two methods for measuring admixture proportions by use of gene identity probabilities was examined. The results suggest that neither procedure has been correctly applied, and that underlying statistical difficulties limit their reliability.     

Admixture and skin color in the transplanted Tlaxcaltecan population of Saltillo,Mexico

Ethnohistoric accounts and serological analyses have documented the genetic effects of transplantation and admixture of several subpopulations of Tlaxcaltecans in Saltillo, Mexico. Interpopulational affinities are assessed using skin reflectance readings taken at the upper inner arm site with a Photovolt Model 670 reflectance spectrophotometer for these groups, focusing on the barrios of La Minita and Chamizal. Genetic distance analyses based on blood groups and skin reflectance data are in close agreement and reflect differential rates of admixture for these groups. Admixture estimates for a dihybrid model (Indian-Spanish) were derived from skin reflectances and show a slight tendency for underestimation of Spanish admixture when compared to blood group estimates. Application of a trihybrid model incorporating West African admixture shows similar estimates based on blood groups, immunoglobulins, and skin color.     

我国部分地方鸡种肤色伴性遗传初步观察

对泰和鸡、仙居鸡、固始鸡、北京油鸡、萧山鸡、狼山鸡（Ｎ系）进行肤色伴性遗传观察,结果表明：泰和鸡常染色体上含有１对黑色素基因ＰＰ,仙居鸡、萧山鸡、北京油鸡性染色体上含有Ｉｄ抑制色素基因,狼山鸡、固始鸡、泰和鸡性染色体上含有ｉｄ基因,泰和鸡♂与含有Ｉｄ基因鸡种（仙居鸡、萧山鸡、北京油鸡）♀杂交,Ｆ１代肤色能自别雌雄,公鸡为黄皮肤,母鸡为黑皮肤。     

Population structure and admixture in transplanted Tlaxcaltecan populations

The history of the Indian populations from the Valley of Tlaxcala since the Spanish conquest of Mexico has been one of fission and transplantation. A number of Tlaxcaltecan families were relocated by the Spanish and founded new communities such as Saltillo and Cuanalan outside the Valley of Tlaxcala. The contemporary genetic structure of these people reflects their ethnohistory. Genetic distances between Tlaxcaltecan groups are the result of differential systematic pressure acting upon them.     

A deterministic model of admixture and genetic introgression: the case of Neanderthal and Cro-Magnon

There is an ongoing debate in the field of human evolution about the possible contribution of Neanderthals to the modern human gene pool. To study how the Neanderthal private alleles may have spread over the genes of Homo sapiens, we propose a deterministic model based on recursive equations and ordinary differential equations. If the Neanderthal population was large compared to the Homo sapiens population at the beginning of the contact period, we show that genetic introgression should have been fast and complete meaning that most of the Neanderthal private alleles should be found in the modern human gene pool in case of ancient admixture. In order to test/reject ancient admixture from genome-wide data, we incorporate the model of genetic introgression into a statistical hypothesis-testing framework. We show that the power to reject ancient admixture increases as the ratio, at the time of putative admixture, of the population size of Homo sapiens over that of Neanderthal decreases. We find that the power to reject ancient admixture might be particularly low if the population size of Homo sapiens was comparable to the Neanderthal population size.     

Gene frequencies and admixture estimates in a Mexico City population

Five hundred and ten students of the Universidad Nacional Autónoma de México were tested to determine the distribution of ABO, MN, Rr-Hr blood groups, and serum haptoglobin, albumin, and Factor Bf types. Based on the results we found that the proportion of Indian and White genes are of 56.16 and 43.84%, respectively in the dihybrid model and 2.93, 56.22, and 40.85% for Blacks, Indians, and Whites in the trihybrid one. The present study reveals a higher proportion of Indian genes in the Mexico City population than estimated in previous publications. Reasons why the present results apply to a much larger group of Mexico City mestizos than the previous ones are given.     

Gene frequencies and admixture estimates in the state of Puebla, Mexico

Three hundred ninety-three individuals from the Universidad Autónoma de Puebla and its University Hospital were studied to determine the distribution of ABO, MN, Rh-Hr, Duffy, and Diego blood groups; red cell hemoglobin and glucose-6-phosphate dehydrogenase variants; and serum haptoglobins, albumins, and factor Bf types. With the results we estimated that the proportions of black, indian, and white genes are 10.7%, 56.3%, and 33.0%, respectively, in a trihybrid model. Reasons are given as to why the black ancestry may be artifically high, and it is pointed out that independent confirmation with other markers is needed before the figure can be accepted as a true value.     

Intertribal gene flow between the Ye'cuana and Yanomama: genetic analysis of an admixed village

Genetic exchange with a neighboring village of Ye'cuana Indians had introduced two alleles, Dia and ACPa, into the Yanomama Indian Village of Borabuk. After several generations, these alleles had reached frequencies of 0.08 and 0.10, respectively. These frequencies are puzzling because they are higher in Borabuk than in the Ye'cuana village from which they were derived. Single allele estimates of ancestral proportions obtained from either of these traits are biologically unrealistic and suggest that admixture is not a good explanation for genetic variation in Borabuk. Nevertheless, multiallelic admixture models are seen to produce credible estimates of ancestral proportions and to explain a large amount of allele frequency variation in Borabuk. When these results are compared with expectations derived froma formal pedigree analysis, good agreement is seen. Comparison of single allele estimates of ancestral proportions obtained from alleles at 11 loci, with multiallelic estimates obtained from the same 11 loci and with the pedigree-derived estimates, demonstrates the superiority of the multiallelic approach.     

Size reduction associated with brachymesophalangia-5: a possible selective advantage

The skin reflectance characteristics of a group of Quechua Indians have been described with an emphasis upon the effects of varying degrees of hybridization, sex and age. This group of Peruvian Indians occupied a reflectance range common to that of all other reported groups of South American Indians. Miscegenation with European Whites had a statistically significant although small influence upon skin color. In general males were consistently darker than females on the three body sites measured. A significant darkening on unexposed body areas occurred in both sexes during early adolescence which may have been caused by the high activity level of the pituitary gland at that stage of the growth cycle.     

Genetic variation in Arizona Mexican Americans: estimation and interpretation of admixture proportions

Mexican Americans are a numerous and fast growing ethnic population in the United States. Yet little is known about their genetic structure. Since they are a hybrid, it is of interest to identify their parental populations and to estimate the relative contributions of these groups. This information is relevant to historical, biomedical, and evolutionary concerns. New genetic typings on 730 Arizona Mexican Americans for the HLA-A, HLA-B, ABO, Rh, MNSs, Duffy, Kidd, and Kell loci are presented here and they are used to estimate ancestral contributions. We considered both a dihybrid model with Amerindians and Spaniards as proposed ancestors, and a trihybrid model with Amerindians, Spaniards, and Africans as proposed ancestors. A modified weighted least squares method that allows for linkage disequilibrium was used to estimate ancestral contributions for each model. The following admixture estimates were obtained: Amerindian, 0.29 +/- 0.04; Spaniard, 0.68 +/- 0.05; and African, 0.03 +/- 0.02. The interpretation of these results with respect to Amerindian and Spanish ancestry is straightforward. African ancestry is strongly supported by the presence of a marker of African descent, Fy, despite the fact that the standard error of the estimate is as large as the estimated admixture proportion. An evaluation of the sensitivity of these results to a number of variables is presented: 1) our choices of ancestral allele frequencies, 2) the possibility of selection at HLA and the blood groups, and 3) genetic drift in Mexican Americans.     

Uncontrolled admixture and loss of genetic diversity in a local Vietnamese pig breed

The expansion of intensive livestock production systems in developing countries has increased the introduction of highly productive exotic breeds facilitating indiscriminate crossbreeding with local breeds. In this study, we set out to investigate the genetic status of the Vietnamese Black H'mong pig breed by evaluating (1) genetic diversity and (2) introgression from exotic breeds. Two exotic breeds, namely Landrace and Yorkshire used for crossbreeding, and the H'mong pig population from Ha Giang (HG) province were investigated using microsatellite markers. Within the province, three phenotypes were observed: a White, a Spotted and a Black phenotype. Genetic differentiation between phenotypes was low (0.5-6.1%). The White phenotypes showed intermediate admixture values between exotic breeds and the Black HG population (0.53), indicating a crossbreed status. Management practices were used to predict the rate of private diversity loss due to exotic gene introgressions. After 60 generations, 100% of Black private alleles will be lost. This loss is accelerated if the admixture rate is increased but can be slowed down if the mortality rate (e.g., recruitment rate) is decreased. Our study showed that a large number of markers are needed for accurately identifying hybrid classes for closely related populations. While our estimate of admixture still seems underestimated, genetic erosion can occur very fast even through indiscriminate crossbreeding.     

New conversion formulae for light-skinned populations using photovolt and E.E.L. reflectometers

Recent research in Belize revealed that published conversion coefficients for use between the two most commonly used reflectance spectro-photometers were inadequate when applied to dark-skinned populations. New research in Ireland shows that the published conversion coefficients for light-skinned populations are also inadequate. A total of 320 school children from Longford, Ireland were measured for skin reflectances at the upper inner arm site with the Photovolt Model 670 and the E.E.L. Reflectance Spectrophotometers. Six and nine filters respectively were used to sample the visible spectrum. Multiple regression techniques were then used to estimate new conversion coefficients which accurately predict readings for one instrument by using some or all of the measurements from the other. Double cross-validation techniques showed the inadequacy of the old (1967) formulae and the very high accuracy of the new ones. Some problems encountered in this study, but not in the one which produced new formulae for dark-skinned populations, suggest further work may be necessary. Additional independently sampled light-skinned populations have not been measured on both machines, so conclusive cross-validation of the new coefficients must remain tentative. Despite this drawback, the new formulae presented here are almost certainly an improvement over the old ones. These new conversion formulae may allow previously impossible comparisons of worldwide data on similar populations.     

Effects of English admixture and geographic distance on anthropometric variation and genetic structure in 19th-century Ireland

The analysis of anthropometric data often allows investigation of patterns of genetic structure in historical populations. This paper focuses on interpopulational anthropometric variation in seven populations in Ireland using data collected in the 1890s. The seven populations were located within a 120-km range along the west coast of Ireland and include islands and mainland isolates. Two of the populations (the Aran Islands and Inishbofin) have a known history of English admixture in earlier centuries. Ten anthropometric measures (head length, breadth, and height; nose length and breadth; bizygomatic and bigonial breadth; stature; hand length; and forearm length) on 259 adult Irish males were analyzed following age adjustment. Discriminant and canonical variates analysis were used to determine the degree and pattern of among-group variation. Mahalanobis' distance measure, D2, was computed between each pair of populations and compared to distance measures based on geographic distance and English admixture (a binary measure indicating whether either of a pair of populations had historical indications of admixture). In addition, surname frequencies were used to construct distance measures based on random isonymy. Correlations were computed between distance measures, and their probabilities were derived using the Mantel matrix permutation method. English admixture has the greatest effect on anthropometric variation among these populations, followed by geographic distance. The correlation between anthropometric distance and geographic distance is not significant (r = -0.081, P = .590), but the correlation of admixture and anthropometric distance is significant (r = 0.829, P = .047). When the two admixed populations are removed from the analysis the correlation between geographic and anthropometric distance becomes significant (r = 0.718, P = .025). Isonymy distance shows a significant correlation with geographic distance (r = 0.425, P = .046) but not with admixture distance (r = -0.052, P = .524). The fact that anthropometrics show past patterns of gene flow and surnames do not reflects the greater impact of stochastic processes on surnames, along with the continued extinction of surnames. This study shows that 1) anthropometrics can be extremely useful in assessing population structure and history, 2) differential gene flow into populations can have a major impact on local genetic structure, and 3) microevolutionary processes can have different effects on biological characters and surnames.     

The use of nonmetric variation in estimating human population admixture: a test case with Brazilian blacks, whites, and mulattos

Measurements in populations which serve as valid indicators of biological relationship should be proportional to genetic distance. In order to test the utility of discrete cranial traits for estimating genetic distances among populations, estimates of admixture are obtained for gene frequency data and nonmetric cranial data in São Paulo mulattos (M). The gene frequency data serve as a control that the three populations are related as stated: estimates of admixture are obtained by using São Paulo whites (W) and blacks (B) as parental populations and by estimating the parameter of admixture, m, in the model p_M = (1 ? m) p_W + mp_B (Elston, 1971) where the p's are either gene frequencies or nonmetric trait frequencies. A test of goodness of fit of the model provides a means of ascertaining whether or not the data fit this linear model. While the gene frequency data indicate distances among the three populations which are highly compatible with the linear model of admixture, the nonmetric data show significant deviations from the model. This implies that the frequencies of the nonmetric traits in the populations used in this analysis are not a linear function of genetic distance. This discourages the use of nonmetric traits in making quantitative conclusions about genetic relationships. It also suggests the need for investigation of the use of other skeletal characters for estimating genetic distance, as well as approaches for such investigations through the study of hybrid individuals.     

Taxonomy and phylogenetics: Some considerations

The relationships between taxonomy and phylogenetics are discussed. It is suggested that they are distinct biological subdisciplines and some consequences of this position are set out.