Admixture studies in Latin America: from the 20th to the 21st century

The present study is a review of admixture studies in Latin America, an interesting subject because of the unique history of the area, in which populations from 3 different origins had contact and intercrossed. The most often used methods of analysis of admixture in Latin America and some problems related to them, such as the determination of the parental populations and selection of genetic markers, are briefly reviewed. Several sources of data for admixture studies (surnames, quantitative traits, proteins, and molecular information) are summarized. The results obtained using protein systems and blood groups, the most often used markers in Latin America, are considered. They are classified according to their application in 3 groups of populations: urban centers, native Americans, and African-descended subjects. The data show that almost every population is dihybrid or trihybrid, and when African influence is not detected, it is probably due more to the method than to an absence of that contribution. A special section is dedicated to the direction of gene flow, and results about directional mating based on mtDNA, Y-chromosome, and nuclear DNA or proteins are also given. From these studies it is possible to conclude that Amerindian admixture came mainly from female lineages, but it is difficult to establish what happened with the African contribution. A last subject considered is the relation between interethnic crosses and diseases; it is easy to analyze that relation when the pathological condition is related to a unique allele, but when complex diseases are considered, the results are not as clear because of the influence of nongenetic factors. Finally, the perspectives for admixture studies in the 21st century are considered, and some attempts to predict their future in Latin America are made.