NCIt definition : The regular and simultaneous occurrence of alternative nucleotide sequences at equivalent
locations of the genetic material among individuals of a single interbreeding population
that are not maintained by recurrent mutation. Polymorphisms may range in size from
single nucleotide to large nucleotide sequence variation visible at the chromosomal
level.;
Alternative definition : NCI-GLOSS: A common change in the genetic code in DNA. Polymorphisms can have a harmful
effect, a good effect, or no effect. Some polymorphisms have been shown to increase
the risk of certain types of cancer.;