DNA Profiling (Edexcel International A Level Biology): Revision Note

DNA Profiling

• A DNA profile can be produced using the process of gel electrophoresis; the result is a series of bands of DNA of different length which can be seen due to the addition of radioactive or fluorescent labels

• DNA profiles can be used to determine the genetic relationships between people, e.g. in paternity tests

  • During a paternity test the DNA profile of a child is compared with a variety of candidates that could be the potential father

  • If many bands of the child's DNA profile match with the bands in a paternity candidate's profile, this could indicate that they are the most likely biological father

    • During fertilisation half of the DNA comes from each parent, so a child will share half of their DNA with a parent

    • When comparing DNA profiles the more bands that match between the profiles, the greater the genetic similarity between those individuals and the closer the relationship

DNA profiles can be compared to determine relationships in paternity testing. Here the child shares bands 1, 3 and 5 with the mother and bands 2, 4 and 6 with candidate B, so he is the most likely father

• DNA profiling is a useful tool in forensic science where it can be used to link possible suspects to a crime scene

  • Regions of DNA, known as short tandem repeats, are examined

    • These short tandem repeats are a type of non-coding, repeated sequence of bases known as a variable number tandem repeat, or VNTR; short tandem repeats consist of short repeating sections, and are also known as micro-satellites

  • The greater the number of these regions examined, the more reliable the evidence provided

    • If only a few regions are analysed then there is a greater chance that closely related individuals will have an identical profile; an analysis of 11 or more sites is considered to be reliable evidence in a law court

DNA profiles can be created using DNA samples found at crime scenes and then compared with the profiles of suspects to show who was present at a crime scene. VNTRs are shown beneath each individual in blue and green; different individuals have different numbers of VNTRS. In this example the DNA profile of suspect 3 is the closest match with the DNA found at the crime scene, though none of the suspects is a perfect match.

• DNA profiling can also be useful in selective or captive breeding programmes of animals or cultivation of plants

  • DNA profiles of the particular organisms can be compared to determine which are genetically the most different from each other

  • These organisms will then be crossbred, ensuring that the individuals that breed together are not closely related

    • Breeding between closely related individuals is known as inbreeding, and can cause genetic problems at an individual and population level

      • In individuals there can be an accumulation of harmful recessive alleles that might otherwise have been masked by healthy dominant alleles

      • Inbreeding leads to a smaller gene pool within a population, which can reduce a population's ability to adapt to change