DNA Fingerprinting - PowerPoint PPT Presentation

DNA Fingerprinting

A Method of Forensic Identification

• 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

• 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 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.

• 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.

• 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

• 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.

• The bigger fragments are near the top

• 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