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DNA Fingerprinting

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DNA Fingerprinting. What is DNA Fingerprinting ?. A technique used to identify people using samples of their DNA.

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What is DNA Fingerprinting?

  • A technique used to identify people using samples of their DNA

Every person has two unique fingerprints: the pattern on their fingertips, and the pattern of their DNA. Fingerprints can be altered by surgery, but a person’s DNA fingerprint is the same in every one of their cells. 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.

Fingerprinting website

who invented it
Who Invented it?
  • The process of DNA fingerprinting was invented by Alec Jeffries at the University of Leicester in England in 1984.
  • He was knighted in 1994.
steps of dna fingerprinting
Steps of DNA Fingerprinting

Step 1:

  • A sample of DNA is taken from
  • Cells are then broken down to release their DNA
  • Blood
  • Hair follicles
  • Saliva
  • Semen
  • Body tissue cells, such as cheek epithelial cells
Step 2: Cutting, sizing and sorting

The DNA is cut into fragments using restriction enzymeswhich cut the DNA at a specific base sequence.

Restriction enzymeanimation

The enzyme EcoRI cutting DNA at the base sequence GAATTC.


DNA fragments are then sorted according to size using a process called gel electrophoresis.

DNA fragments are injected into wells in agarose gel (a jelly-like product made from seaweed) and an electric current is applied along the gel.

DNA is negatively charged so it is attracted to the positive end of the gel.

The shorter DNA fragments move faster than the longer fragments.

Gel electrophoresis animation


Step 3: The DNA fragments are transferred to a nylon sheet by placing the sheet on the gel and soaking them overnight.

Step 4: A radioactive material is added which combines with the DNA fragments to produce a fluorescent image.

A photographic copy of the DNA bands is then made.

Step 5:
  • The pattern of fragment distribution is then analysed.

In a standard DNA fingerprint, about a dozen sites are analyzed, with each site having many possible alleles.

The chance that two patterns will match is incredibly small: 1 in 30 million (except for identical twins).


A DNA Fingerprint

Suspect’s shirt

Examine the DNA fingerprints at the right. A man with blood on his shirt was arrested for murder. He claimed that he had cut himself, and the blood was his. Is he lying or telling the truth?

Suspect’s DNA 

DNA detective animation

HGP fingerprinting page

uses of dna fingerprinting
Uses of DNA Fingerprinting

Forensic science (solving crimes)

For example:

A murder victim is found. The forensics team retrieved a blood sample from the crime scene. They prepared DNA fingerprints of the blood sample, the victim and a suspect as follows:

was the suspect at the crime scene
Was the suspect at the crime scene?

Suspect’s Profile

Blood sample from crime scene

Victim’s profile

famous cases
Famous Cases
  • Colin Pitchforkwas the first criminal caught based on DNA fingerprinting evidence.
  • He was arrested in England in 1987 for the rape and murder of two girls, and was sentenced in 1988.
famous cases1
Famous Cases
  • O.J. Simpsonwas cleared in 1994 of a double murder charge which relied heavily on DNA evidence.
  • This case highlighted the lab difficulties and handling procedure mishaps which can cause such evidence to be significantly doubted .

Famous Cases

In 1994, Royal Canadian Mounted Police detectives successfully tested hairs from a cat known as Snowball, and used the test to link a man to the murder of his wife, thus marking for the first time in forensic history the use of non-human DNA to identify a criminal.

Yup, he did it.


Paternity and maternity testing

DNA fingerprints can be used to determine whether a particular person is the father (paternity) or mother (maternity)of a child.

This information can be used in

  • Paternity suits
  • Inheritance cases
  • Immigration cases

In the 1920s, Anna Anderson claimed that she was Princess Anastasia Romanov of Russia. In the 1980s after her death, samples of her tissue that had been stored at a Charlottesville, Virginia hospital following a medical procedure were tested using DNA fingerprinting and showed that she bore no relation to the Romanovs.


Who’s your daddy?





 Examine each set of DNA fingerprints above.

 Determine if each alleged father is, in fact, the father of the child. If the child and man share the same allele, the man is the father.

famous paternity cases
Famous paternity cases
  • In 2002 Elizabeth Hurley used DNA fingerprinting to prove that Steve Bing was the father of her child Damien.
  • In 2007 DNA fingerprinting was used to determine that Larry Birkhead was the biological father of Anna Nicole Smith’s daughter Dannielynn.

personal identification in the armed services(instead of dogtags, dental records or blood types)

 identifying human remains.For example, many of the victims of the 9/11 terrorist attack were identified by DNA fingerprinting.


Medical Uses of DNA Fingerprinting

matching organ donorsto people needing an organ replacement.

 diagnosing inherited disordersin prenatal and newborn babies.

research on genetic disorders.

as well as…

 studying populations of wild animals


Whose blood is it?

Whose hair is it?

Other forensics problems




Blood stain