02-01-2013, 12:41 PM
DNA fingerprinting
DNA fingerprinting.ppt (Size: 756.5 KB / Downloads: 40)
Historical background
DNA fingerprinting was developed in 1984
by Alec. J. Jeffrey at the University of Leicester
He was studying the gene of myoglobin.
What is DNA Fingerprinting?
The chemical structure of everyone's DNA is the same.
The only difference between people (or any animal) is the order of the base pairs.
The information contained in DNA is determined primarily by the sequence of letters along the zipper.
The different sequence
Using these sequences, every person could be identified solely by the sequence of their base pairs
there are so many millions of base pairs, the task would be very time-consuming
Instead, scientists are able to use a shorter method, because of repeating patterns in DNA.
These patterns do not, however, give an individual "fingerprint,"
they are able to determine whether two DNA samples are from the same person, related people, or non-related people.
DNA Fingerprinting using VNTR's
On some human chromosomes, a short sequence of DNA has been repeated a number of times.
the repeat number may vary from one to thirty repeats
these repeat regions are usually bounded by specific restriction enzyme sites
cut out the segment of the chromosome containing this variable number of tandem repeats (VNTR's )
identify the VNTR's for the DNA sequence of the repeat.
Making DNA Fingerprints
DNA fingerprinting is a laboratory procedure that requires six steps:
1: Isolation of DNA.
2: Cutting, sizing, and sorting.
Special enzymes called restriction enzymes are used to cut the DNA at specific places
3: Transfer of DNA to nylon.The distribution of DNA pieces
is transferred to a nylon sheet
by placing the sheet on the gel
and soaking them overnight.
4-5: Probing.Adding radioactive or colored probes to the nylon sheet produces a pattern called the DNA fingerprint.
Criminal Identification and Forensics
DNA isolated from blood, hair, skin cells, or other genetic evidence left at the scene of a crime can be compared
FBI and police labs around
the U.S. have begun to use
DNA fingerprints to link suspects
to biological evidence –
blood or semen stains, hair,
or items of clothing
Considerations when evaluating DNA evidence
In the early days of the use of
genetic fingerprinting as criminal
evidence, given a match that had a
1 in 5 million probability of occurring
by chance the lawyer would argue
that this meant that in a country
of say 60 million people there were 12 people
who would also match the profile.
Technical Difficulties
Errors in the hybridization and probing process must also be figured into the probability
Until recently, the standards for determining DNA fingerprinting matches, and for laboratory security and accuracy which would minimize error