Variable Number Tandem Repeats (AQA A Level Biology): Revision Note

Variable number tandem repeats

• Variable number tandem repeats (VNTRs) are regions found in the non-coding sections 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 recognition 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