Using gene map science to evaluate the genetic map and eliminate disease

Genetic Map Markers and Linkage Analysis

You know how an interstate map can guide you from one city to another. A genetic map is like that, and it guides researchers toward their target gene. Just as there are landmarks in interstate maps, there also are landmarks in genetic maps known as genetic markers.

Scientists use several types of markers: restriction fragment length polymorphisms (RFLP), variable number of tandem repeat polymorphisms (VNTR), microsatellite polymorphisms, and single nucleotide polymorphisms (SNP). The marker which may soon be more meaningful to you is the SNP.

Three companies recently announced plans to market genetic testing services to individuals. Their technology employs SNPs (also called 'snips'). Each SNP represents a tiny difference in your genome. The SNP is a mutation involving only one nucleotide.

Although two genes are found on the same chromosome, they are not always inherited together. The linkage between them is thus only partial. It is during meiosis (the production of female eggs and male sperm), as chromosomes split and exchange DNA sections, where genes continue to be linked (thus inherited) or not. This exchange is known as crossover or recombination.

Researchers cannot count the number of crossovers that happen. But they can work back what happened during meiosis and identify the neighboring markers. They then subject their data to statistical analysis called genetic linkage studies. Linkage analysis allows researchers to make reasonable, statistically valid inferences of the crossover patterns that occurred, and consequently the probable order of SNPs and other markers involved, plus the probability that markers may recombine.

Linkage analysis may correctly give the order of markers, but the distance between two markers cannot always be correctly determined. Linkage analysis results become valuable inputs to genetic sequencing, a more precise genetic map similar to the street maps in individual cities.



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Genetic Linkage Map

A chromosome map showing the relative positions of the known genes on the chromosomes of a given species.