5.6- Genetic Fingerprinting

  • Created by: Rebecca
  • Created on: 21-06-11 22:13

The Technique of Genetic Fingerprinting:

  • All individuals have different sequences of what is known as non-functional DNA (DNA with no known function).
  • They consist of 20-40 base long sequences that are long and are often repeated many times. 
  • These unique length of non-coding DNA are known as hyper-variable regions (HVR) or short tandem repeats (STRs), and are passed on to the offspring. 
  • It is the number of times that these lengths repeat themselves that is used to show differences between individuals:
  • First the DNA is cut into fragments by restriction endonuclease.
  • They are then separated by electrophoresis, and the negatively charged fragments move to the positively charged end of the trough containing gel and exposed to an electric current. The smaller ones move faster, so they separate by size.
  • The fragments are transferred onto the nylon membrane of the trough by southern blotting.
  • Radioactive probes bind at certain point on fragments.
  • Fragments exposed when put under X-Ray, and are separated into dark (a dark band indicates where an electrical probes is present) and light bands.
  • These patterns are called a person's genetic fingerprint and is different for every individual.
  • The bands in a fingerprint are inherited from both parents: these can be used in paternity suits and can also be used to convict criminals.
  • To to this, white blood cells are taken from the mother and the possible father. The bands of the mother are subtracted from the child's pattern. If the man is the true father, he must possess all the remaining bands in the child's genetic fingerprint.

Gene Amplification Using the POlymerase Chain Reaction (PCR):

  • PCR techniques are often used for crime scene investigations, where only small fragments of DNA can be found, and large numbers of tests need to


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