Genetic polymorphism

A genetic polymorphism is the existence of two or more variants - which may be allelic, phenotypic, chromosomal or general DNA sequence variants - at significant frequencies in a population. A frequency of 1% or more is generally considered to be a polymorphism.

Types of polymorphism include:

  • Single nucleotide polymorphisms (SNPs) where there is a change in one nucleotide. These are very common in the human genome, with a single-nucleotide sequence variant occurring roughly once every 100-300bp, on average
  • Restriction fragment length polymorphisms (RFLPs, or 'rif-lips') is variation in the length of a fragment produced on digestion with restriction enzymes. This is due to mutations which move the restriction site about

Genetic polymorphisms can be useful as genetic markers, allowing us to home in on the genetic locus for certain inherited diseases.