SNP Variants Encyclopedia

Single nucleotide polymorphisms (SNPs, pronounced "snips") are the most common type of genetic variation in the human genome. With over 10 million SNPs identified across the 3.2 billion base pairs of human DNA, these single-letter changes account for approximately 90% of all human genetic variation and form the foundation of modern genetic testing and personalized medicine.

Each SNP represents a position in the genome where a single nucleotide (A, T, C, or G) differs between individuals or between paired chromosomes within an individual. SNPs are cataloged using "rs numbers" — unique identifiers assigned by the dbSNP database at the National Center for Biotechnology Information (NCBI). When you receive your raw data from a DNA testing service, your file contains hundreds of thousands of these rs-numbered variants along with your personal genotype at each position.

The clinical significance of SNPs varies enormously. Some, like rs334 (the sickle cell variant in the HBB gene), have dramatic, well-understood effects on health. Others, like rs4680 (COMT Val158Met), have moderate effects that interact with lifestyle and environmental factors. The vast majority of SNPs have no known clinical significance — they are simply markers of human diversity and ancestry. The challenge and opportunity of genomic medicine lies in distinguishing which variants matter for you personally.

Several SNP variants have become particularly well-known due to their broad health implications and accessibility through consumer testing. rs1801133 (MTHFR C677T) affects folate metabolism and homocysteine levels, with implications for cardiovascular health and pregnancy outcomes. rs9939609 (FTO) is the most replicated obesity-associated variant. rs7412 and rs429358 together determine your APOE genotype (E2, E3, or E4), influencing both cardiovascular and Alzheimer's disease risk. rs6025 (Factor V Leiden) is the most common inherited blood clotting disorder. rs12913832 in the HERC2 gene is the primary determinant of blue versus brown eye color — a vivid demonstration of how a single nucleotide can shape visible traits.

When interpreting SNP results, several concepts are essential. Allele frequency tells you how common each variant is in different populations. The minor allele frequency (MAF) indicates whether a variant is rare (<1%), low-frequency (1–5%), or common (>5%). Effect size, often expressed as an odds ratio, quantifies how much a variant increases or decreases risk. And zygosity — whether you carry one copy (heterozygous) or two copies (homozygous) of a variant — often determines the strength of its effect through dominant, recessive, or additive inheritance patterns.

Through Ask My DNA, you can explore your personal SNP profile across hundreds of clinically annotated variants, understand what your genotypes mean in the context of current scientific evidence, and discover actionable insights about your genetic predispositions — all through an intuitive AI-powered conversation interface.