Definition:

"A genetic marker is defined as a specific gene or DNA sequence that produces a detectable trait with a known location on a chromosome and that can be used to study family and population, identification of cells, species or individual".

Introduction:

Genetic marker can also be described as a variation (or a change that may be arising due to alteration or mutation in the chromosome locus). It may be a short sequence of DNA, for example single nucleotide polymorphism or SNP (genetic variation in a DNA sequence that occurs when a single nucleotide in a genome is altered; SNPs are usually considered to be point mutations that have been evolutionarily successful enough to recur in a significant proportion of the population of a species), or a long sequence, such as mini-satellites (is a section of DNA that consists of a short series of bases 10-60 bp).

Background:

In the past, most organisms were limited in gene mapping (is defined as graphical representation of the arrangement of genes on a chromosome) by genetic markers these includes genes that translate observable features, for example blood types or seed shapes.

Types:

There are numerous types of genetic markers that are commonly used;

• Simple Sequence Length Polymorphism or SSLP: This is used as a genetic marker with polymerase chain reaction or PCR (used to produce multiple copies of DNA). It is a type of polymorphism (is the existence of two or more forms of individuals within the same animal species) and repeated sequences in intergenic regions of DNA. Genetic variation between two individuals can be understood by using length of SSLPs.

• Restriction Fragment Length Polymorphism or RFLP: It is a technique that uses variations in DNA sequences. In this technique, sample of DNA is broken into small pieces with the help of restriction enzyme. Then these small pieces will be separated according to their lengths by gel electrophoresis (that separates molecules on the basis of their rate of movement through a gel). RFLP is an important tool in localizing genes for genetic disorder (), genome mapping, finding of risk for disease, and paternity testing (is the use of genetic fingerprinting to determine whether two individuals have a biological parent-child relationship).

• Amplified Fragment Length Polymorphism or AFLP: It is a PCR-base tool. It is used in different fields such as genetics, DNA fingerprinting (or DNA testing, DNA typing is a technique employed by forensic scientists to assist in the identification of individuals by their respective DNA profiles) and genetic engineering.

• Random Amplification of Polymorphic DNA or RAPD: It is a type of polymerase chain reaction but in this case DNA segments that are amplified would be random. It has been used to trace the phylogeny (is the sequence of events involved in the evolutionary development of a species or taxonomic group of organisms) of various animals and plants.

• Single Nucleotide Polymorphism or SNP: It is a segment of DNA sequence in the genome. In other words, it is a genetic variation that occurred when a single nucleotide A, T, C, or G is altered in a genome. Most commonly SNPs have only two alleles.

• Variable Number Tandem Repeat or VNTR: It is located in a genome where nucleotide sequence is arranged as tandem repeat. These repeats can be found on many chromosomes. VNTR analysis is useful and important in genetics, forensics, biology research and DNA fingerprinting.

• Short Tandem Repeat or STR: It occurs in DNA when two or more nucleotides are repeated. These repeated sequences are immediately adjacent to each other. In forensic cases, STR analysis is used for determining genetic profiles.

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