A-LEVEL BIOLOGY AQA NOTES
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- Genetic fingerprinting is a method used to produce a specific pattern of DNA bands from an individual’s genome.
- The non-coding regions of DNA contain short, repeating sequences called variable number tandem repeats (VNTRs).
- VNTRs are found at many locations in the genome. In every individual, they vary in length and the in the number of repeats at different loci. Therefore, the probability of two individuals having the same VNTRs is very low.
- The steps in DNA fingerprinting include:
- Extraction of DNA & amplification using PCR
- DNA digestion using specific restriction endonucleases, leaving the VNTRs intact
- Separation of DNA fragment by gel electrophoresis. Smaller fragments travel faster and therefore move further down the gel
- Hybridisation of the VNTRs at specific (complementary) base sequences with Radioactive or fluorescent DNA probes
- Development. The banding pattern can then be visualised as radiation, emitted by fragments, exposes X-ray film (placed over the gel) and reveals their final positions.
- The DNA profiles can be compared to determine genetic relationships by looking for similarities in the banding pattern.
- DNA profiles can also be used in:
- Forensic science investigations- comparing the DNA profiles of suspects and DNA at the crime scene.
- Medical diagnosis- DNA profiles can identify individuals at risk of developing specific diseases, as some VNTRs are correlated with an increased risk of disease e.g. Huntington’s disease
- Animal and plant breeding- DNA profiles are used to prevent inbreeding by not breeding individuals with similar profiles
- Paternity determination- half the DNA profile of the child should match the father