The first map of copy-number variation in the human genome has been created. It is now feasible to examine the role of such genome variation in disease and to explore in depth the extent of 'normal' variability. The Human genome contains many forms ofgenetic variation. The most plentiful are the millions of single base-pair changes in the DNA code that were identified in the course of determining the human genome sequence, and then more systematically through the International HapMap Project. Theseso-called single nucleotide polymorphisms (SNPs) distinguish any two unrelated copies of the genome. They account for the long-hypothesized, evolution-arily 'neutral' forms of widespread genetic variation that mark diversity within our species, as well as mutations, both rare and common, that account for or contribute to disease.
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