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Sunday, January 06, 2008

Microsatellite sequence is Short sequence (2-5) repeat DNA

014. Microsatellite sequence is:

1. Small satellite.

2. Extra chromosomal DNA.

3. Short sequence (2-5) repeat DNA.

4. Looped-DNA.

Answer

3. Short sequence (2-5) repeat DNA.

Reference:

Harrison 16th Edition Page 449

Robbins 7th Edition Page 307

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Harrison

Discussion

Microsatellites are tandem repeats of one to six nucleotides scattered throughout the genome

Explanation

Ä "Microsatellites" are defined as loci (or regions within DNA sequences) where short sequences of DNA (nucleotides; adenine - A, thiamine - T, guanine - G, cytosine - C) are repeated in tandem arrays. This means that the sequences are repeated one right after the other. The lengths of sequences used most often are di-, tri-, or tetra-nucleotides.

Ä

Comments

Ä A microsatellite consists of a specific sequence of DNA bases or nucleotides which contains mono, di, tri, or tetra tandem repeats. For example,

o AAAAAAAAAAA would be referred to as (A)11

o GTGTGTGTGTGT would be referred to as (GT)6

o CTGCTGCTGCTG would be referred to as (CTG)4

o ACTCACTCACTCACTC would be referred to as (ACTC)4

Ä In the literature they can also be called simple sequence repeats (SSR), short tandem repeats (STR), or variable number tandem repeats (VNTR). Alleles at a specific location (locus) can differ in the number of repeats. Microsastellites are inherited in a Mendelian fashion.

Tips

Because microsatellites are widely dispersed in eukaryotic genomes, are highly variable, and are PCR based (requiring only minute amounts of starting template) they have been used in many different areas of research such as:

Ä Forensics- Microsatellite loci, generally known in forensic applications as Short Tandem Repeat (STR) loci, are widely used for forensic identification and relatedness testing, and are a predominant genetic marker in this area of application. In forensic identification cases, the goal is typically to link a suspect with a sample of blood, semen or hair taken from a crime. Alternatively, the goal may be to link a sample found on a suspect's clothing with a victim. Relatedness testing in criminal work may involve investigating paternity in order to establish rape or incest. Another application involves linking DNA samples with relatives of a missing person. Because the lengths of microsatellites may vary from one person to the next, scientists have begun to use them to identify criminals and to determine paternity, a procedure known as DNA profiling or "fingerprinting". The features that have made use of microsatellites attractive are due to their relative ease of use, accuracy of typing and high levels of polymorphism. The ability to employ PCR to amplify small samples is particularly valuable in this setting, since in criminal casework only minute samples of DNA may be available.

Ä Diagnosis and Identification of Human Diseases- Because microsatellites change in length early in the development of some cancers, they are useful markers for early cancer detection. Because they are polymorphic they are useful in linkage studies which attempt to locate genes responsible for various genetic disorders.

Ä Population Studies- By looking at the variation of microsatellites in populations, inferences can be made about population structures and differences, genetic drift, genetic bottlenecks and even the date of a last common ancestor.

Ä Conservation Biology- Microsatellites can be used to detect sudden changes in population, effects of population fragmentation and interaction of different populations. Microsatellites are useful in identification of new and incipient populations.

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