Applied Genetics Group at NIST (characterization of genetic polymorphisms)

Polymorphisms are variations in a person’s DNA sequence. These may occur in an exon and result in a difference in the protein derived from that gene. The variations may alternativley reside in an intron and have no impact on the formation of the protein from that gene. 

A polymorphism is a genetic variant which has arisen in a distant common ancestor and is therefore not unique to an individual or taht individual’s immediate family. Forty per cent of women in the general female population, for example, have one or more polymorphisms in the BRCA1 gene that are not found in the remaining 60% of the population. About 1 in 800 women in the general femaile populaiton has a mutation in the BRCA1 gene sequence that places her at high genetic risk of developing breast cancer and ovarian cancer. 

Most of the genetic diversity among members of an individual species comes about through meiosis and genetic recombination. The greater the distance between two loci on a single chromosome, the greater is the chance that they will be separated by crossing-over occurring at a site between them. If two genes are reassorted in x% of gametes, they are said to be separated on a chromosome by a genetic map distance of x map units.

Short tandem repeats (STR): See outline

Hypervariable microsatellite sequence/Variable number of tandem repeat (VNTR): are repeated DNA sequences such as CACACA found in various positions (loci) in the human genome. The number of repeats can be highly variable in the population, ranging from 4 to 40 in different individuals. Because of the variability in these sequences at each locus, individuals usually inherit a different variant from their mother and father. Such VNTRs are used in forensic science to identify potential criminal suspects. When examining the variability at 5-10 different VNTR loci, the odds that two random individuals would share the same genetic pattern by chance is about one in 10 billion. More complex sequences called Minisatelites such as GATTCCTTn vs GATTCCTTn can also be repeated.