SNP (Single Nucleotide Polymorphism)
Definition
A position in the genome where the nucleotide base differs between individuals. Genome-wide SNP panels are more powerful than STR panels for population assignment because thousands of informative loci can be assayed simultaneously.
- Type
- Single base variation in the DNA sequence at a defined genomic position
- Main forensic uses
- Ancestry determination, phenotyping, degraded-sample analysis
- Advantage over STRs
- Thousands of SNP loci can be analyzed at once, providing greater power for population assignment
Common questions
What is an SNP and why does it matter in forensics?+
An SNP is a single base variation at a specific location in the DNA sequence where different people carry different nucleotides. Forensic labs use SNPs for ancestry, phenotyping (predicting physical traits), and analyzing samples that are degraded or fragmented, where other DNA tests might fail.
How are SNPs better than STRs for determining someone's origin?+
SNP panels can assay thousands of informative loci simultaneously across the genome, giving far more geographic power than STR panels. This lets forensic scientists assign a person to a population or region much more reliably because they're using many more markers at once.
Can SNPs help when DNA is damaged or old?+
Yes. SNPs are useful for degraded-sample work because single base variations can often be detected and read even when DNA is fragmented or partially broken down, whereas some other genetic markers require longer intact stretches of DNA.
Related terms
- Autosomal vs Mitochondrial DNA
- Autosomal DNA is nuclear, biparentally inherited, present as two copies per cell. Mitochondrial DNA is cytoplasmic, maternally inherited, present in hundreds to...
- Capillary Electrophoresis
- Size separation of fluorescently labelled PCR products through a polymer-filled capillary on an instrument like the ABI 3500. Output is an electropherogram.
- Chromosome
- A discrete, condensed structure consisting of a single long DNA molecule complexed with histone proteins. Humans normally carry 46 chromosomes in 23...
- CODIS
- The FBI's Combined DNA Index System, the US national STR-based forensic DNA database. Contains profiles from convicted offenders, arrestees, and unidentified crime-scene...
- Delta-C13 / Delta-N15
- Stable carbon and nitrogen isotope ratios in tissue, expressed as deviation from a reference standard (delta notation). They reflect diet composition and...
- Isoscape
- A map of isotope ratio variation across a geographic area, derived from systematic sampling of soil, water, plant, or mineral material; used...
- Multiplex STR Kit
- Single-tube PCR amplifying 15+ STR loci plus amelogenin in one reaction. AmpFISTR Identifiler Plus and PowerPlex are the workhorses in Indian DNA...
- Nucleotide
- The monomer unit of nucleic acids. Each nucleotide consists of a five-carbon sugar (deoxyribose in DNA, ribose in RNA), a phosphate group,...
- PCR
- Polymerase Chain Reaction. Kary Mullis 1983. Exponential amplification of a target sequence using a thermostable Taq polymerase, two primers and thermal cycling.
- Population Structure
- The non-random distribution of genetic variation across subpopulations caused by limited gene flow between them. Different elephant herds separated by geography or...
- RFLP
- Restriction Fragment Length Polymorphism. The first-generation DNA typing method using restriction enzymes and Southern blotting. Required nanograms of intact DNA.
- STR (Short Tandem Repeat)
- A genomic locus where a 2, 7 base-pair unit is repeated in tandem a variable number of times between individuals. The variation...
Explained in these topics
- DNA in Forensic Science: Structure, Genetic Markers, Extraction and ProfilingA single-base variation at a defined position. Used for ancestry, phenotyping, and degraded-sample work.
- Population Genetics, Geographic Provenance, and Stable IsotopesA position in the genome where the nucleotide base differs between individuals. Genome-wide SNP panels are more powerful than STR panels for population assignm...