Natural variations in a gene, DNA sequence, or chromosome
that have no adverse effects on the individual and occur with fairly high
frequency in the general population
Definition from: GeneReviews
from the University of Washington and the National Center for Biotechnology Information
Polymorphism involves one of two or more variants of a particular DNA sequence. The most common type of polymorphism involves variation at a single base pair. Polymorphisms can also be much larger in size and involve long stretches of DNA. Called a single nucleotide polymorphism, or SNP (pronounced "snip"), scientists are studying how SNPs in the human genome correlate with disease, drug response, and other phenotypes.