More than 99% of the genome sequence is identical across the human population. SNPs reflect the small sequence variations (often a single base change) that can occur within an individual gene. It is important to note that SNPs do not change much from generation to generation. Human genome sequencing projects have identified more than 2 million SNPs as genetic markers. Most SNPs are found outside of coding sequences, but some SNPs found within a coding sequence are of particular interest to researchers, because the change may alter the biological function of a protein. Because of the enormous potential to associate SNP maps with the development of complex diseases such as cancer, Alzheimer's, diabetes, and hypertension, researchers are feverishly working to identify thousands of useful SNP markers. For example, SNPs in the breast cancer genes 1 and 2 are associated with the development of breast cancers (Freedman et al., 2005). SNPs in the apolipoprotein E gene have been linked to a higher risk of developing Alzheimer's disease (Bullido et al., 1998). One of the goals in this field is to generate arrays that are capable of genotyp-ing thousands of polymorphisms in a single hybridization. This may someday allow for the construction of an individual's genetic fingerprint that will be able to predict individual risk for developmental disorders and diseases. After this technology emerges, we can also anticipate the discussion of social and ethical issues associated with the use of this information.
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