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DNA Fingerprinting. A Method of Forensic Identification. How do you figure out that someone’s DNA is more similar to another’s?. The primary method of assessing similarities is by use of DNA fingerprinting or DNA restriction analysis.

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DNA Fingerprinting

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dna fingerprinting

DNA Fingerprinting

A Method of Forensic Identification

how do you figure out that someone s dna is more similar to another s
How do you figure out that someone’s DNA is more similar to another’s?
  • The primary method of assessing similarities is by use of DNA fingerprinting or DNA restriction analysis.
  • This process makes use of special proteins called restriction enzymes and sections of the chromosome called tandem repeats
tandem repeats
Tandem Repeats
  • A region of the chromosome that contains multiple copies of a core DNA sequence that are arranged in a repeating fashion
  • Repeats act as fillers or spacers between coded sections of DNA
  • All humans have the same type of repeats but there is tremendous variation in the number of repeats that each of us has.
restriction enzymes
Restriction Enzymes
  • Restriction enzymes cut DNA but only at a certain combination of A, G, T, and C.
  • Different restriction enzymes cut DNA at different places—each has a unique sequence it recognizes.
  • The restriction enzyme EcoRI cuts DNA at the sequence GAATTC and will cut only at that sequence.
restriction fragment length polymorphisms rflp
Restriction Fragment Length Polymorphisms (RFLP)
  • RFLPs are different fragment lengths of base pairs that result from cutting a DNA molecule with a restriction enzyme
  • It is the length differences associated with DNA strands or RFLPs that allow one to distinguish one person from another.
an example using ecor i for a question of paternity
An Example Using EcoR I for a Question of Paternity
  • EcoR I cuts a similar section of DNA on Bob, Larry, and Mary
  • After the cut how many fragments Bob, Larry, and Mary have?
  • Answer: 2, 3, and none

Recall: EcoR I cuts only at GAATTC

example con t
Example Con’t
  • After the DNA is cut with EcoR I, Bob’s, Larry’s and Mary’s fragments are placed in different lanes on an agarose gel
  • The fragments are then subjected to an electric field
  • The smaller fragments move faster, the larger ones move slower
  • This process of separating the fragments by length is called electrophoresis.
resulting picture after electrophoresis
Resulting Picture after Electrophoresis
  • The bigger fragments are near the top
paternity test
Paternity Test
  • In general the child’s DNA must be a combination of Mary’s DNA and one of the men. Which man is the father?
  • Answer: Larry