SC.912.L.16.11

Forensics and DNA fingerprinting

Discuss the technologies associated with forensic medicine and DNA identification, including restriction fragment length polymorphism (RFLP) analysis.

DNA Extraction:

DNA can be extracted from almost any human tissue.•Buccal cells from inside cheek for paternity tests.

•Sources of DNA at crime scene: blood, semen, hair follicle, saliva.

•DNA extracted from evidence is compared to DNA from known individuals

•Extracted DNA molecules are incubated with restriction enzymes (endonucleases).Restriction enzymes are

produced by bacteria as a defense against viruses.These enzymes cut DNA at specific base sequences called recognition sites.Results in smaller pieces of DNA called RFLP’s.

An EcoR1 restriction enzyme

RFLP Analysis:

•RF stands for Restriction Fragments. Those are the fragments that were cut by restriction enzymes.•L stands for Length, and refers to the length of the restriction fragment.•P stands for Polymorphisms, a Greek term for “many shapes”. The lengths of some of the restriction fragments differ greatly between individuals.RFLP = Restriction Fragment

Length Polymorphism

Molecular biologists have identified regions of the human genome where restriction fragment lengths are highly variable between individuals.

Electrophoresis of these RFLP’s produce different patterns of DNA bands.With 3 billion base pairs in the human genome, however, RFLP analysis would produce a ‘smear’ of many similar sized fragments.

Gel ElectrophoresisDNA is cut into

fragments using an enzyme

The cut DNA is put on a Gel material

An electric current is applied on the Gel

DNA is negatively charge

DNA fragments will start moving towards the positively charged side

Smaller fragments move faster

After some time, we have a separation of the different fragment lengths

DNA “fingerprint”

DNA “fingerprint”A radioactive

material is added which combines with the DNA fragments to produce a fluorescent image.

A photographic copy of the DNA bands is obtained.

•The RFLP markers most commonly used for DNA profile analysis are found on chromosomes 1, 2, 4, 5, 10 and 17.

•These RFLP markers are named after their locations on these chromosomes.

•For example, the marker on chromosome 2 is called D2S44 (section 44 of chromosome 2).

•These chromosomal locations are also referred to as DNA loci.

RFLP Analysis:

Solving Medical ProblemsDNA profiles can be used to determine

whether a particular person is the parent of a child.

A childs paternity (father) and maternity(mother) can be determined.

This information can be used in• Paternity suits• Inheritance cases• Immigration cases

Famous Case…O.J. Simpson was

cleared of a double murder charge in 1994 which relied heavily on DNA evidence.

This case highlighted lab difficulties.