Genetic polymorphism and fertility parameters in the Aymara of Chile and Bolivia

Natural fertility in northeastern Mexico: genetic structure by year of birth and birthplace

BACKGROUND

The aims of this population genetics study were 1) to ascertain whether 417 Mexican women with natural fertility (45 years of age, married, not using any family planning methods, residing in the state of Nuevo León) were genetically homogeneous, and 2) to compare the genetic structure of this selected population with the previously reported data of random populations of northeastern Mexico.

METHODS

A sample of 417 women was interviewed and selected in seven medical units of the Mexican Social Security Institute. They were grouped by their year of birth (1896-1925 and 1926-1955) and birthplace [persons whose four grandparents were born in the northeastern states (NE) and outside the northeastern states (Not-NE) of Mexico]. Eight genetic marker systems were analyzed.

RESULTS

Gene diversity analysis suggests that more than 99.1% of the total gene diversity can be attributed to variation between individuals within the population. Genetic admixture analysis suggests that this selected population, stratified by year of birth and birthplace, have received a predominantly Spanish contribution followed by a lesser Mexican Indian contribution.

CONCLUSIONS

The genetic structure of this selected population was homogeneous and similar to the random populations of northeastern Mexico. This finding corroborates the utility of this selected population for genetic and epidemiological studies.

Biochemical heterozygosity and phenotypic variability of polygenic traits

Using the theory of additive genetic variability of a polygenic trait, it is shown that an individual's heterozygosity at the loci governing the trait cannot be determined accurately from observations on phenotypes alone. Furthermore, the negative association between heterozygosity and phenotypic variance, and a positive correlation of the frequency of the modal class of a phenotypic trait and the extent of heterozygosity can be explained by additive allelic effects. It is argued that while the number of heterozygous loci in an individual may not be a good indicator of the individual's genomic heterozygosity, there is evidence that some of the biochemical loci may reflect genetic variation at the loci controlling phenotypic polymorphism. Thus the observed relationship between biochemical heterozygosity and phenotypic variance may not constitute hard evidence of heterosis, overdominance, or associative overdominance.