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Polymorphism

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Definition:

A combination of the Greek words poly (meaning multiple) and morph (meaning form), this term is used in genetics to describe the multiple forms of a single gene that can exist in an individual or among a group of individuals. Gene sequencing studies, like that done for the human genome project, have revealed that, at the nucleotide level, the gene encoding a specific protein can have a number of differences in sequence. These differences don't alter the overall product significantly enough to produce a different protein, but may have an effect of substrate specificity and specific activity (for enzymes), binding efficiencies (for transcription factors, membrane proteins, etc.) or other features and functions. For example, within the human race, there are many different polymorphisms of CYP 1A1, one of many cytochrome P450 enzymes of the liver. Although the enzymes are basically the same sequence and structure, polymorphisms in this enzyme can influence how humans metabolize drugs. The use of genetic polymorphisms was one of the strengths of deCODE Genetics, a company that focused on determining genetic risk factors for various diseases.

Examples:
CYP 1A1 polymorphisms in humans, where, in exon 7 the Isoleucine amino acid is replaced by Valine, has been linked to smoking-related lung cancer.

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