Molecular Basis of Inheritance Test - 13

In specific regions of DNA sequence, a small stretch of DNA is repeated many times. The repetitive DNA are separated from bulk genomic DNA during density gradient centrifugation.

Genome variations are differences in the sequence of DNA from one person to the next

In human’s 99.9% of the base sequences of DNA are same & are referred as Bulk genomic DNA.

The difference lies in remaining 0.1%. It is these differences which make every individual unique in their phenotypic appearance. This DNA has small stretches of repetitive sequences. They are referred as Repetitive DNA.

Satellite DNA contains short nucleotide sequences repeated thousands of time tandemly. Satellite DNA is divided into different categories according to their size i.e., micro-satellites, mini-satellites etc. 

• Micro-satellite consists of 2 – 6 bp repeats.
• Mini-satellite consists of 10 – 100 bp repeats, they are referred as VNTRs.

These sequences generally do not code for any protein.

Polymorphism is variation at genetic level which occurs due to mutation. Polymorphisms are inheritable from parent to children without any changes so DNA fingerprinting is the basis of paternity testing.

The sensitivity of fingerprinting technique has been increased by use of Polymerase chain reaction (PCR). After that single cell obtained from organism is enough for this technique.

VNTR analysis (sometimes called DNA fingerprinting) can be used to identify and match cell samples.

In order to use VNTRs, we must have a source of DNA. The DNA can come from any nucleated cell, e.g., white blood cells, skin samples, semen samples, or hair folicles. Red blood cells cannot be used as they do not have a nucleus.

For a VNTR analysis, the DNA is extracted and cut using restriction endonucleases. A Southern Blot is then performed using various probes.

Amplification is a mechanism leading to multiple copies of a chromosomal region within a chromosome arm.

The DNA amplification technique of the polymerase chain reaction (PCR) is a laboratory method for creating multiple copies of small segments of DNA.

DNA finger printing is highly reliable method of identification of individual involved in crimes. DNA a fingerprinting is a sure method in solving paternity and maternity disputes.DNA fingerprinting cannot be used to cure HIV infection.

A Southern blot is a method used in molecular biology for detection of a specific DNA sequence in DNA samples. Southern blotting combines transfer of electrophoresis-separated DNA fragments to a filter membrane and subsequent fragment detection by probe hybridization.

VNTR of two persons may be similar at certain sites but could be different at other sites because a child inherits 50% of chromosomes from mother and remaining 50% from father. VNTR genes also undergoes different kinds of mutations.