An organism’s genome contains many repetitive, non-coding base sequences. The probability of two individuals having the same repetitive sequences is very low. The technique of genetic fingerprinting in analysing DNA fragments, that have been cloned by PCR, and its use in determining genetic relationships and in determining the genetic variability within a population. Candidates should be able to - explain the biological principles that underpin genetic fingerprinting techniques - interpret data showing the results of gel electrophoresis to seperate DNA fragments - explain why scientists might use genetic fingerprints in the field of forensic science, medical diagnosis, animal and plant breeding.

Introns (parts of DNA that don't code for anything) are made up of repeating units called core sequences. Because every individual (apart from identical twins) had unique DNA, it is most likely that no two people will have the same core sequences.

 

This is the process of genetic fingerprinting:

• Extraction: and then replication using PCR
• Digestion: by restriction endonucleases
• Separation: by gel electrophoresis; then alkali used to separate into single strands
• Southern blotting; the strands are transferred on to a nylon membrane by absorbent sheets drawing them up by capillary action; fixed with UV
• Hybridisation: marked probes (radioactive or fluorescent) are then added at specific temperatures and PHs to bind to specific core sequences
• Development: if the probes are radioactive the pattern is transferred to x-ray film

The film or gel will then show a unique pattern of lines corresponding to the DNA.

 

Uses:

• Forensics: comparing the genetic fingerprint of a suspect and DNA from a crime scene to see if they are from the same person (probability of the results being the same but from different people is calculated)
• Medical diagnosis: if done with genes patients DNA can be compared to that of someone with a disease to see how similar they are thus how likely they are to get it (e.g. Huntington's); DNA from pathogens from a patient can be compared with that of known ones to find out what it is
• Breeding: to identify desirable or undesirable genes
• Determining genetic variability: if DNA from different animals of the same species is very similar there is little genetic variability
• Paternity testing: if you have the DNA of a mother next to the DNA of her child and the DNA of someone who may or may not be the father, everywhere the DNA of the child does not match with the mother, it will match with the father if he is the real one