showed a median difference of 15 to 20 percent at both the microsatellite and SNP markers. Additionally, 10 percent of all markers showed a difference of 40 percent or more. To the extent that findings from this study reflect the larger population, one would hypothesize that an allele with 20 percent or greater frequency in one racial group would also be found in another racial group, while those with a frequency below 20 percent would most likely be race-specific.

According to Burchard (2003), “race-specificity of variants is particularly common among Africans, who display greater genetic variability than other racial groups and have a larger number of low-frequency alleles.” Burchard concludes that variation among racial groups in the occurrence of variant alleles underlying disease or normal phenotypes may lead to differences in occurrence of the phenotypes themselves. For example, in some studies of hypertension, variation of SNPs at different allelic frequencies from one population to another suggest that higher rates of hypertension found in African Americans may be related to the alternations in DNA that vary by group (Cui et al., 2003; Erlich et al., 2003). Prior to drawing conclusions, however, one must consider alternative explanations that include gene-environment interactions as possible contributors to observed disparities (Whitfield and McClearn, 2005).

Arguments that genetic factors cannot be a major cause of health disparities arise out of a paradigm of genetic research that focuses on independent effects of genetics. Research on health disparities is an important opportunity to integrate biological knowledge with social and behavioral knowledge in order to better understand the determinants of disease. Social factors are certainly key contributors, but there is evidence that those factors do not account for all health differences (Braun, 2002). Conversely, solely focusing on molecular genetics ignores the dynamic nature of populations of DNA and the complex relationships among genes, organisms, and environment.

Considerable literature exists concerning how environmental processes, events, and circumstances contribute to development and behavior in ways that influence health as well. Some of these environmental factors are negative and are found to be more prevalent in the development of minorities. Some research suggests that African Americans may experience events and circumstances that have sociocultural origins that significantly influence development over the life course (Levine, 1982; Spencer et al., 1985; McLoyd and Randolph, 1985; Jackson, 1985; Jackson and Chatters, 1986). These sociocultural influences contribute to differences between racial groups as well as to differences between individuals within groups (Krauss, 1980; Levine, 1982; Jackson and Chatters, 1986). Sources of individual differences in health and behavior in African Americans have implications for the quality of late life as well as quantity of late life (years of life



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