What is VNTR?
VNTR or the Variable Number of Tandem Repeats are the repeated DNA sequences at a defined locus. The repeats are clustered together and oriented in the same direction. Individual repeats can be added or removed through replication and recombination errors. This forms alleles with different number of repeats.
The DNA segments vary in different individuals and are hence beneficial in identifying individuals in case of a crime scene or a paternity dispute. This is known as DNA fingerprinting.
The tandem repeat sequences of DNA are also termed as “satellite DNA”. These are of three main types:
Types Of VNTR
These are highly repetitive DNA sequences and each DNA sequence consists of several thousand base pairs. A satellite can measure up to 100 million base pairs. These are found occurring in the regions of heterochromatin. The Y chromosome has abundant satellites. This makes it convenient for the researchers studying paternal genetic transmission in mammals.
The density of the DNA is the function of its base and sequence. The satellite DNA with its highly repetitive DNA has a reduced density compared to the rest of the genome. Therefore, the name “satellite DNA” is coined.
The satellite DNA has several biological functions:
Satellite DNA is present in the centromeric and pericentromeric regions. It regulates the functions of the centromere.
They help in the formation of heterochromatin.
Satellite RNA transcripts are found in plants, vertebrates, and invertebrates
In a minisatellite, each repeat ranges from 9 to 100 base pairs. It is an array of tandem repeats 500 to 300,000 base pairs long.
Minisatellites have been found in association with important features of the human genome such as gene regulation, imprinting, and chromosomal fragile sites. They provided the first highly polymorphic, multiallelic markers for linkage studies.
Most of the minisatellites are GC rich. They possess a strong strand symmetry.
The repeats are very short, 2-6 base pairs each. The whole array ranges from 10,000 to 100,000 base pairs long. They are therefore called short tandem repeats or simple sequence repeats.
They are usually found in insect and plant chromosomes, and euchromatin regions of vertebrates.
Microsatellites are important to the population geneticists because of the variable number of repeats among the individuals of a population.
Microsatellite markers are inherited from both the parents. Therefore, they are useful for paternity tests. Highly polymorphic loci increase our ability for parental analysis.
Microsatellites are not affected by natural selection. But they are influenced by gene flow, genetic drift, and mutation.
Importance of VNTR
VNTRs are found on many chromosomes and vary in length among different individuals. Each variant helps in personal or parental identification.
VNTRs are an important source of genetic marker RFLP which is used in the linkage analysis of genomes. A banding pattern unique to each individual is produced by the VNTRs.
VNTR has its applications in forensic science, DNA fingerprinting, and other genetics and biology researches.
Also read: Chromatin