Each person has two versions of each SNP—one received from each parent. The objective of SNP testing is to identify an individual's allele type for both versions of each of hundreds of thousands of SNPs chosen from across the entire genome.

About SNPs

The Human Genome Project and subsequent 1000 Genomes Project have shown that the sequence of DNA nucleotides from one person to the other varies little. In fact, it is estimated that all humans share about 99.9% identical DNA. To avoid the redundancy and expense of excessive whole genome sequencing, scientists are using a spot check approach to learn about the impact of the differences in the remaining .01%.

Genome sequencing projects have identified millions of single base pair locations on human chromosomes that are polymorphic (poly = variable; morph = form) among humans. The base pairs at those locations (or loci) are called single nucleotide polymorphisms (SNPs).

What are SNPs?

23andme (18 Apr 2012) Genetics (Part 2 of 5): What are SNPs? [Video file] retrieved from https://youtu.be/tJjXpiWKMyA

23andme (18 Apr 2012) Genetics (Part 2 of 5): What are SNPs? [Video file] retrieved from https://youtu.be/tJjXpiWKMyA

Each SNP (usually pronounced snip) represents a difference in a single nucleotide pair. For example, one persons may have the base pair T-A at a specific location on chromosome 16 and another may have the base pair C-G in the same location. To be classified as a SNP, the variation must occur in at least 1% of the population.

Less common variations, those that occur in less than 1% of the population, are called single nucleotide variants or SNVs. In genealogy discussion boards, presentations and blogs you may also hear SNVs called private SNPs. The promise of SNVs as individual family markers is being embraced by genetic genealogists with optimism. Private SNPs are especially promising for Y chromosome surname projects where there is a need to characterize and sort individual lines of descent from a common male line ancestor. There are roughly 10 million SNPs spread throughout the human genome. They occur about once in every 300 nucleotides and are most commonly found in regions between genes as opposed to within protein coding or regulatory regions.

A SNP arises as a mistake or mutation during DNA replication. On extremely rare occasions, as DNA polymerase moves along a growing nucleotide chain, it mistakenly inserts the wrong nucleotide pair and a SNV results. If that happens during the process of meiosis, the SNV will be passed down to the offspring. From there, the SNV may be passed to future generations and eventually become common enough in the population (>1%) to be classified as a SNP. With 3 billion base pairs in the human genome, the likelihood of the same mutation occurring at the same locus more than once is extremely low. In fact, it is thought that SNPs are so rare that each human SNP has occurred only once in human history. For example, the SNP that is responsible for all the blue eyes in the world is thought to have occurred only once. All blue eyed people in the world descend from that person.

When SNPs do fall within coding or regulatory regions of DNA, they may play a direct role in the expression of traits or diseases that are affected by that gene’s function. Genome Wide Association Studies (GWAS) have been successful in finding genetic variations that contribute to such diseases as asthma, cancer, diabetes, heart disease and mental illness.

Most SNPs are functionally neutral. They have no effect on traits, health or development. Nevertheless, those SNPs are proving to be very useful as biological markers for nearby genes. Such SNPs may predict risks of developing certain diseases, responses to drugs, and susceptibilities to toxins.

Because SNPs are inherited they are also very useful for defining or verifying family lines and relationships. Ancestry Informative Markers (AIMs) are SNPs that differ in allele frequencies across different populations. Most such variations are shared by members of the same population so a high frequency of that allele will be a characteristic of the population. These SNPs are used in ethnicity predictions to distinguish between people of different geographic and cultural backgrounds.

There are many many more SNPs to explore!

Where Can I Go From Here?

Contexo.info is a not for profit, educational website.

©️2002 - 2017 Context.info

Where Can I Go From Here?

©️2002 - 2017 Context.info

Contexo.info is a not for profit, educational website.

My Image