Single nucleotide polymorphism

Single nucleotide polymorphism (often abbreviated to SNP) is a variation in a single nucleotide that occurs at a specific position in the genome, where each variation is present to some appreciable degree within a population (e.g. > 1%).

Overview

A single nucleotide polymorphism (SNP) is the most common type of genetic variation among people. Each SNP represents a difference in a single DNA building block, called a nucleotide. For example, a SNP may replace the nucleotide cytosine (C) with the nucleotide thymine (T) in a certain stretch of DNA.

SNPs occur normally throughout a person’s DNA. They occur almost once in every 1,000 nucleotides on average, which means there are roughly 4 to 5 million SNPs in a person's genome. These variations may be unique or occur in many individuals; scientists have found more than 100 million SNPs in populations around the world.

Function

Most SNPs have no effect on health or development. Some of these genetic differences, however, have proven to be very important in the study of human health. Researchers have found SNPs that may help predict an individual’s response to certain drugs, susceptibility to environmental factors such as toxins, and risk of developing particular diseases. SNPs can also be used to track the inheritance of disease genes within families.

Types

There are two types of SNPs: transversion and transition. Transversion is the replacement of a purine for a pyrimidine or vice versa. Transition is the replacement of a purine for another purine or a pyrimidine for another pyrimidine.

See also

• Genome-wide association study
• Genetic variation
• Genotyping
• Human genome

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