ABSTRACT
T he history of North America has been marked by the encounter of populations from different continents. The discovery of the New World began a period defined by human migrations at a much larger scale than in previous history. This movement of people, voluntary or forced, changed profoundly the human landscape. As populations came into contact, admixture followed in varying degrees depending on the circumstances. Today, many people living in the US, Mexico, Canada and the Caribbean can trace their ancestry to more than one continent. The most important genetic contributions came from the indigenous Native American groups, Western Europeans and West Africans, although there have also been influences from other regions, such as East Asia and South Asia. We can reconstruct and inter pret this history of migration and admixture using genetic markers. A very complete perspective can be obtained when analyzing autosomal markers (located on any of the chromosomes other than the sex-determining chromosomes, which are inherited from both parents), maternally transmitted mtDNA markers and Y-chromosome markers, which are transmitted from fathers to sons. In many cases, the maternal and paternal admixture histories are remarkably different, so including mtDNA and Y-chromosome markers can provide a much better picture than that offered by the autosomal markers. Thus, using genetic markers we can reconstruct history at the individual and population level, even in the absence of a historical record. In this chapter, I provide an overview of admixture in North America, with a particular emphasis on the two major admixed groups: African Americans (and African Caribbeans) and Hispanics. I also dis cuss the implications of the history of admixture for the distribution of the genetic variation involved in drug metabolism and drug response and the potential consequences of population stratification in candidate gene association studies in recently admixed populations.
