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Cardiovascular diseases (CVD) have the highest worldwide mortality rate of any type of disease. In recent years, genetic research regarding CVD has been conducted using association studies, in which the presence of a genetic polymorphism associated with a specific cell signaling pathway in a lower or in a higher frequency among patients may be interpreted as a possible causal factor. Genetic polymorphisms that occur in the β-adrenergic receptor 1 (β-ADR1) can result in significant changes in its function that may result in physiopathologies. Ambiguous categorizations, such as skin color and self-reported ethnicity have been used in pharmacogenetic studies as phenotypic proxies for ancestry; however, admixed populations present a particular challenge to the effectiveness of this approach. The main objective of the present study was to estimate the diversity and the frequency of the Ser49Gly polymorphism of the β-ADR1 gene in a sample of 188 male individuals from the population of Rio de Janeiro. The Ser49Gly frequencies were analyzed by two forms of sample stratification: The phenotypic criterion of black or non-black skin color, and African or non-African ancestry, defined using Y-chromosome single nucleotide polymorphisms and autosomal indel markers. These results were used to evaluate whether marker-based ancestry criteria and/or skin color were associated with the frequency of the Ser49Gly polymorphisms in the heterogeneous Rio de Janeiro/Brazilian population. The DNA fragments of interest were amplified by polymerase chain reaction with specific primers for the Ser49Gly marker, and genotyping reactions were performed by restriction with the enzyme Eco0109I. Heterozygosity values ranging from 0.25 to 0.50 and 0.20 to 0.41 were found for the groups stratified by ancestry and skin color, respectively. Using the Hardy-Weinberg equilibrium at the ser49Gly marker, it was found that there was no significant deviation in the genotype distribution of the whole Rio de Janeiro sample or the stratified sample. Analysis of the allelic distribution in the Rio de Janeiro population sample revealed frequencies of 80.30 and 19.70% for the wild-type (Ser49) and mutated (Gly49) alleles, respectively. Significant differences were observed in the allele frequencies of the Ser49Gly marker between the self-defined black and non-black phenotype, and the African and non-African descendant genotype population samples. A significant difference was also observed between blacks and African-descendant individuals, with a lesser degree of genetic differentiation. The results presented in the present study suggest that the Ser49Gly marker has a distribution that is influenced by an ancestral component, due to the increased prevalence of the Gly49 polymorphism in the black and African descendant populations of the Rio de Janeiro state. This evidence, in combination with clinical studies, may contribute to a detailed analysis of the pattern of susceptibility to CVD involved in β-ADR1 receptor mechanism failure. [ABSTRACT FROM AUTHOR]