DNA Fingerprinting

Dr.L.Yatawara

Dept. of MLS, FAHS,UoP

Dr.L.Yatawara

DNA Fingerprinting can be used in paternity testing or murder cases.

Dr.L.Yatawara

DNA Fingerprint Basics

• Different individuals carry different alleles.

• Most alleles useful for DNA fingerprinting differ on the number of repetitive base sequences they contain.

• Restriction enzymes are used to cut the DNA along these repetitive sequences.

Dr.L.Yatawara

DNA Fingerprint Basics

• If DNA is cut with a restriction enzyme that recognizes sites on either side of the region that varies, DNA fragments of different sizes will be produced.

• A DNA fingerprint is made by analyzing the different sizes of DNA fragments produced from a number of different sites that vary within the genome.

Dr.L.Yatawara

DNA Fingerprint Basics

DNA fragments of different size will be produced by a restriction enzyme that cuts at the points shown by

the arrows.

Dr.L.Yatawara

DNA fragments are then separated based on size

using gel electrophoresis.

Dr.L.Yatawara

Results

• In a standard DNA fingerprint, as many as a dozen sites can be analyzed with each site having many possible combinations of alleles.

• When many genes are analyzed, each with many different alleles the chance that two sites will match is 1 in 100 billion when no lab err is factored in.

Dr.L.Yatawara

A DNA fingerprint from a murder case

Dr.L.Yatawara

A DNA fingerprint from a paternity test

Dr.L.Yatawara

Unlike a conventional fingerprint that occurs only on the fingertips and can be altered by surgery, a DNA fingerprint is the same for every cell, tissue, and organ of a person. It cannot be altered by any known treatment. Consequently, DNA fingerprinting is rapidly becoming the primary method for identifying and distinguishing among individual human beings.

Dr.L.Yatawara

An additional application of DNA fingerprint technology is the diagnosis of inherited disorders in adults, children, and unborn babies.

Dr.L.Yatawara

DNA Fingerprinting

It was at 9am on Monday September 15, 1984 when Sir Alec Jeffreys removed some X-ray film from its

developing tank that he experienced a rare, serendipitous moment in science.

He had been looking for good genetic markers for

basic genetic analysis, but had accidentally stumbled upon a way of establishing a human's

genetic identification.

Dr.L.Yatawara

His technique has subsequently been applied to a wide range of problems in genetics. These include developing genetic markers for medical research and the diagnosis of inherited disorders:

Dr.L.Yatawara

DNA fingerprinting is also used in the solving of crimes, establishing family relationships - for example in paternity and immigration disputes, and also in breeding programs in a number of zoos and conservation centers to establish family relationships within captive colonies of endangered species of animals and birds to minimize inbreeding and maintain genetic diversity.

Dr.L.Yatawara

Fingerprinting a Crime Suspect

There are three basic components to a DNA fingerprint test.

•First, there is the DNA from the crime scene; •Second, there is the DNA from a suspect; •Third, there is DNA with known attributes that is used as a control. Dr.L.Yatawara

Problems with DNA Testing

Many have questioned the validity of DNA fingerprinting test results. Because the burden of proof is on the forensic scientists, there are safeguards in place to be sure that DNA fingerprinting results are accurate. The first is the control DNA that runs through the tests alongside the suspect's DNA and the DNA found at the crime scene. If the control DNA tests properly, then the DNA in question tested properly as well. Another safeguard in place is that the test is run four times using four different restriction enzymes. In order to be absolutely positive of a match, all four sets of DNA from the crime scene must match all four sets of DNA from the suspect.

Dr.L.Yatawara