Biology (Year 12)
DNA profiling is a technique used by scientists to identify an individual by comparing an unknown sample of DNA with known DNA profiles. An alternative name for DNA profiling is DNA fingerprinting. In DNA profiling, the scientist looks for a match within the non-coding (junk) regions of an individual's genome. This 'junk DNA' is made up of:
Short Tandem Repeats (STRs): Short, repeating sequences of nucleotide bases 4-8 nucleotides long
Variable Nucleotide Tandem Repeats (VNTRs): Longer, repeating sequences of nucleotide bases longer than 5 nucleotide bases in length
Non-coding regions of DNA contain these types of "satellite DNA", i.e. long stretches of DNA made up of STRs and VNTRs. Individuals of the same species (usually) contain unique banding patterns of DNA which make up their STRs and VNTRs, reflecting their unique genetic information. These banding patterns are visualised via gel electrophoresis and compared with known DNA profiles to distinguish between individuals.
DNA fingerprinting begins with isolating a sample of DNA from an organisms' somatic cell; a specific fragment is cut using restriction enzymes at a specific recognition site
PCR is used to amplify the sample DNA (which is too small for analysis)
Gel electrophoresis allows scientists to separate fragments, visualise their length and the number of repeats; smaller fragments have less STRs and migrate further and faster during electrophoresis
DNA is visualised under a UV light
The profile is complete, and shows a unique set of patterns of bands; the patterns of bands are all different among differing individuals due to processes in sexual reproduction
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