Definition
What is a single nucleotide polymorphism?
A SNP, pronounced "snip", is a site in the DNA sequence where one base varies among members of a population: at a given position, for example, some people carry a C and others a T. To count as a polymorphism rather than a rare mutation, the less common version is usually expected to be fairly frequent, traditionally carried by at least 1 percent of the population.
SNPs are the most frequent type of variation between people. On average there is about one every 1,000 bases, adding up to roughly 4 to 5 million in a typical person's genome, and more than 600 million have been found across world populations. Most lie in DNA between genes and have no known effect. Those inside a gene or its control regions can change a protein or how much of it is made.
Because they are common and easy to test, SNPs serve as markers for tracing inheritance and finding regions linked to disease. Genome-wide association studies compare SNPs across thousands of people to find variants tied to conditions such as diabetes and heart disease, and some SNPs predict how a person responds to certain drugs.
Word parts
Where does the term “single nucleotide polymorphism” come from?
- poly-
- manyGreek polys
- morph-
- form, shapeGreek morphe
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Terms that go with it
- Genome-wide association studyA genome-wide association study (GWAS) scans the genomes of many people to find genetic variants that are more common in those with a trait or disease.
- MutationA mutation is a lasting change in an organism's DNA sequence, ranging from a single altered base to large rearrangements of chromosomes.
- AlleleAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
- NucleotideA nucleotide is a single unit of DNA or RNA, made of a nitrogen-containing base, a five-carbon sugar and one or more phosphate groups.
- GenomeA genome is the complete set of DNA in an organism or cell, including all of its genes and the stretches of DNA between them.
- GenotypeA genotype is the genetic makeup of an organism, either at one locus, such as Aa, or across its whole genome, including alleles it does not express.
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Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Single Nucleotide Polymorphisms (SNPs)
- MedlinePlus Genetics: What are single nucleotide polymorphisms (SNPs)?
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