Variable Number Tandem Repeats (AQA A Level Biology)

Variable Number Tandem Repeats

• Variable number tandem repeats (VNTRs) are regions found in the non-coding part of DNA

• A short DNA sequence (e.g. GATA) is repeated a variable number of times without any spaces, at a single location

• These VNTRs may be referred to as ‘satellite’ or ‘microsatellite’ DNA

• The length of VNTRs varies between different people

  • The probability that two individuals would have the same length VNTRs is extremely small

  • As a result, VNTRs can be used to identify the source of DNA from tissue samples

• However, the number of VNTRs a person has is inherited

  • They can be used to identify biological parents

• Different restriction enzymes are used to cut the DNA at different base sequences close to the variable number tandem repeat (VNTR) regions

• The distance between recognitions sites of a restriction enzyme will change depending on the number of repeated sequences

• Therefore DNA fragments of different lengths are produced when the same restriction enzymes are applied to different DNA samples

• When these DNA fragments undergo electrophoresis they produce a distinctive pattern

  • Only identical twins will produce an identical pattern of restriction fragments

The restriction endonucleases cut at specific recognition sites located near the repeat sequences. Longer repeat sequences mean that the distance between recognition sites is greater, producing longer DNA fragments. Sample C has the longest repeat region and so produces the longest DNA fragment.