populations. However, most populations share common SNP variants and haplotype patterns, most of which were inherited from the common ancestor population. Frequencies of these SNP variants and haplotype patterns may be similar or different among populations. For example, the gene for blood type is variable in all human populations, but some populations have higher frequencies of one blood type, such as O, while others have higher frequencies of another, such as AB. For this reason, the HapMap consortium needs to include samples from a few geographically separated populations to find the SNP variants that are common in any of the populations.
Charles Rotimi, Ph.D., leader of the Howard University group collecting the blood samples in Nigeria, said, "We need to be inclusive in the populations that we study to maximize the chance that all people will eventually benefit from this international research effort."
Because of the block pattern of haplotypes, it will be possible to identify just a few SNP variants in each block to uniquely mark, or tag, that haplotype. As a result, researchers will need to study only about 300,000 to 600,000 tag SNPs, out of the 10,000,000 SNPs that exist, to efficiently identify the haplotypes in the human genome. It is the haplotype blocks, and the tag SNPs that identify them, that will form the HapMap.
Haplotypes and Health
To date, most of the known disease-causing genetic variations have been for relatively rare disorders, such as Huntington's disease and cystic fibrosis. These diseases are caused by variants in single genes that tend to have a big impact on health, making the genetic contributions to the illnesses relatively easy to find using current methods that rely on gathering family information, or pedigrees.
Researchers face a much tougher challenge when it comes to uncovering the genetic contributors to more common diseases, such as Alzheimer's disease, arthritis, cancer, diabetes, scPage: 1 2 3 4 5 6 7 Related biology news :1
Contact: Geoff Spencer
NIH/National Human Genome Research Institute
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