Single-nucleotide polymorphism

Single-nucleotide polymorphism, also known as SNP, is a tiny change in a gene, or part of a gene. It's like a typing error in the gene. Most of the time, SNPs don't do much and don't cause any problems. But sometimes, a single change in a gene can cause a big change, like affecting how a person looks, or how likely they are to get a certain disease.