Racial Categorization in Human Genetic Variation Research

The completion of the HGP has resulted in new and well-funded themes of scientific inquiry in medicine. A central goal of human genetic research is identifying the genetic and environmental causes of human disease. Recent advances such as high-throughput genomic sequencing technology have increased the efficiency of large-scale rapid genotyping and ushered in a new era of genetic epidemiological research. This research has focused on the identification of single-nucleotide polymorphisms (SNPs). As was discussed briefly above, the genome is specified by the four nucleotide "letters" A (adenine), C (cytosine), T (thymine), and G (guanine) that form patterns. SNP variation occurs when a single nucleotide, such as an A, replaces one of the other three nucleotide letters: C, G, or T. SNPs are believed to be associated with individual differences in susceptibility to disease; environmental insults such as bacteria, viruses, toxins, and chemicals; and drugs and other therapies.

The search for these genetic clues has led to efforts to map SNPs and use that information to identify the multiple genes associated with complex diseases such as cancer, diabetes, vascular disease, and some forms of mental illness. For most SNPs, all populations have all the possible genotypes for a SNP, but populations may differ in regard to the frequencies of individuals with each of the different genotypes.

Although the location of SNPs is believed to hold the key to identifying the genetic basis for the onset of disease and influencing responses to drug therapeutics, it has been posited that SNPs do not travel independently. Instead, SNPs are located in what has been identified as blocks of alleles that are inherited as units. The patterns of the SNP alleles in those blocks are called haplotypes. Studies show that most SNPs are in haplotype blocks that have been transmitted for many generations without recombination. Because each block has only a few common haplotypes, identifying haplotypes eliminates much of the tedious work of attempting to find single SNPs that are correlated meaningfully with disease. In effect, the task of locating frequently elusive needles in the enormous haystack of the human genome has been mitigated by the knowledge that these needles, or SNPs, tend to be located in groups. It is expected that the 10 million common SNPs will be reduced to 200,00 to 300,000 tag SNPs that will signal the location of regions that affect disease more readily through genome scans.

To create a genetic test that will screen for a disease in which the disease-causing gene already has been identified, scientists collect blood samples from a group of individuals affected by the disease and analyze their DNA for SNP patterns. Next, researchers compare those patterns to patterns obtained by analyzing the DNA from a group of individuals not affected by the disease. This type of comparison, which is called a disease gene association study, can detect differences between the SNP patterns of the two groups, indicating which pattern most likely is associated with the disease-causing gene. Eventually, SNP profiles that are characteristic of a variety of diseases will be established. As part of that effort an increasing amount of research has called for the DNA sampling of individuals identified with specific racial minority populations. The collection of DNA samples has resulted in the racial categorization of genetic material stored in governmental and commercial genetic databases.

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