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Pedigree samples were collected from five ethnically and geographically different populations: Kirghizians, Turkmenians, Chuvashians, Israelis and Mexicans. All studied individuals were assessed for body height, weight and BMI. The sample size in the studied pedigrees ranged from 381 to 1811 individuals. Segregation analysis of these traits preliminarily adjusted for sex and age was performed by means of program package MAN that provides parameter estimates for the major gene effects, for the residual within the genotype correlations between relatives and for the assortative mating. By the usual transmission probability tests, the 'environmental' model was strongly rejected for all measured traits in all 5 populations. The major gene mode of inheritance, however, was accepted for all traits. The results of analysis in 5 populations were remarkably similar, and showed that except for Mexican sample, the proportion of variance attributable to major gene effect ranged between 37 and 53% for body weight and height. In the Mexican sample it explained only about 14% of the body weight variation. The proportion of inter-individual variation in BMI attributable to major gene effect was consistently lower in all populations in comparison with height and weight and ranged between 17 and 40%. Strong assortative mating in body height, as estimated by correlation between putative major gene genotypes in spouses, was found in four populations, not including Mexican pedigrees.

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The genetic component in a mixed heritability model, including major gene, multifactorial and sibling environment transmissible components, was studied for some 20 anthropometric traits in two ethnically different samples. The first sample comprised 305 Mexican nuclear families, and the second comprised 83 Ashkenazi Jewish nuclear families living in Israel. All variables, after adjustment for age and sex, were subjected to principal-components analysis (PCA) in each sample separately. The mixed model of inheritance as implemented in the computer program POINTER was used in the present study. An attempt was made to evaluate genetic effects in the variation of the first principal components (PCs). PCA showed a clear separation of variables and was easily interpretable. The PC1 was a credibly general size factor. This factor alone accounted for about 30% of the total variance. Other components are rather shape factors for various combinations of traits. The testing of several genetic hypothesis showed the following: (1) For all factor scores the genetic component was high and statistically significant. (2) In a Mexican sample, for PC1 and PC2, both major gene and polygenes contributed significantly to the total variation of these variables; in the major locus the alleles were most probably codominant. (3) For all other PCs the major gene effect hypothesis was rejected, with more than 50% of the variation attributable to the polygenes contribution. (4) No evidence was found for sibling environmental resemblance in either sample.

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The rate change of gene frequency in a population subject to emigration obviously depends on differences in the effective reproductive size (and resulting random genetic drift effects) between emigrants and natives. An important additional force may be the different selection pressures of the original and the new environment into which the population penetrates. Discrete traits and monolocus systems have been studied in many natural populations of various species. However, knowledge about the migration influence on quantitative, i.e. polygenic, characters is very limited. The present study set out to answer the following biological questions: (1) Does migration induce changes in sets of phenotypic, genetic and environmental correlations? (2) If so, are these changes expressed in levels and/or structure of the correlation matrices? Data on 20 anthropometric traits in 305 Mexican families [129 families from Mexico (sedentary population) and 176 families living in Texas (migrant population)] were used for analysis. The curves of distribution and average values of phenotypic, genetic and environmental correlations remained unchanged between the two populations. However, qualitatively (i.e., as far as the agreement between matrix compositions is concerned), all three matrices changed significantly. The phenotypic correlations appear to be the most highly canalized, the correspondence between the two matrices being 62.1%. The environmental matrices had the highest variation, and although 26.3% of the correlations were in agreement, this was statistically nonsignificant. The most important finding in the present study was the relatively low correspondence between the two genetic matrices (35.6%). We suggest that these changes were provoked by preselection (i.e., by a nonrandom sample) of migrating individuals.

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PIP: Evidence from Mexican-American families regarding the question of balanced selection in anthropometric traits in relation to fertility or "Darwinian fitness" is presented and assessed. The data are organized on the basis of 3 kinds of selection on continuously distributed characters in natural selection: 1) directional, favoring 1 extreme; 2) stabilizing, (balanced), in which the average phenotype has greater reproductive fitness over the extremes; and 3) destabilizing, in which the extremes have the highest Darwinian fitness. There have been marked differences in the results of previous studies on the subjest. The present study is based on data collected in 1941 on Mexican immigrant parents and their American born children in Texas and of parents and children in central nad northern Mexico. At least 1 child in each family had to be an adult. Information was obtained as fully as possible for all children, living and dead. 176 families were studied in Texas and 129 in Mexico. 230 families in which the mother was at least 40 years old were included. Modal, minimal, and maximal classes were established in parental populations (both sexes combined) for morphological traits and for the sexes separately. The variability of fertility was determined according to mprphological class of mother and father separately and their interaction by analysis of variance with 2-factor interchange. The traits: (weight, stature, min. frontal, bizygomatic, bigonial, hand length, hand width, ear index, body surface area, weight/surface ratio) and directional in 10 other parental traits (head length, head width) menton-crinion, menton-nasion, nose height, nose width, ear height, ear width, cephalic index, and nose index), except nose width in the latter group which was in the destabilizing category. The directional traits in regard to mean munber of children were generally in the order of minimal, modal, and maximal class. None of the differences between the means, however, were statistically significant. It has been calculated that a difference of 1% in fertility between 2 groups would require 38,000 families in each group for statistical significance at the 5% level. Whether fertility in the sense of a large number of offspring is a requisite of natural selection in the case of human beings appears to be moot in view of the pervasive influence of "cultural selection" which so significantly mediates mating patterns and family size.^ieng

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Changes in the genetic and environmental components of the phenotypic variance of 20 morphological characters were studied in Mexican migrant and sedentary populations. As far as the changes in variance components and the average values of traits were concerned, it was found that some traits were subjected to different forms of selection pressure, some changed within the limits of the norm reaction, and some remained unchanged.

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