Lab 7 - DNA Fingerprinting and Gel Electrophoresis

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After completing this activity, students will be able to:

• Identify the steps to DNA Fingerprinting• Recognize patterns in DNA, and where the

patterns come from• Describe other ways that DNA Fingerprinting

can be used, besides in crime scene analysis

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What is DNA Fingerprinting?

• A technique used by scientists to distinguish between individuals of the same species using only samples of their DNA

• 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 has been used as the primary method for identifying and distinguishing among individual human beings, since 1987.

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Who Invented it?

• The process of DNA fingerprinting was developed by Alec Jeffreys at the University of Leicester, in England, in 1985.

• He was knighted in 1994, for his service to science and technology.

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• The first step is to obtain a sample of DNA evidence from blood, or other bodily fluid.

• DNA is present in white blood cells of humans, but not red blood cells which lack nuclei.

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Biological materials used for DNA Fingerprinting

• Blood• Hair follicles• Saliva• Semen• Body tissue cells• Hair• Bone• Urine (if it contains

epithelial cells)

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Steps of DNA Fingerprinting• Next, cells are broken

down to release DNA

• If only a small amount of DNA is available it can be amplified (meaning – make lots more of it) using the polymerase chain reaction (PCR)

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• PCR can be used to create thousands or millions of copies of a piece of DNA.

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Steps of DNA Fingerprinting• Then, the DNA is

cut into fragments using restriction enzymes.

• Each restriction enzyme cuts DNA at a specific base sequence.

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Steps of DNA Fingerprinting

• The sections of DNA that are cut out are called restriction fragments.

• This yields thousands of restriction fragments of all different sizes because the base sequences being cut may be far apart (long fragment) or close together (short fragment).

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Steps of DNA Fingerprinting• Fragments are separated

on the basis of size using a process called gel electrophoresis.

• DNA fragments are injected into wells and an electric current is applied along the gel causing the negatively charged fragments to move.

• The gel is made of agarose, a jelly-like substance made out of seaweed that allows the fragments of DNA to pass through. #NSB2014 11

Steps of DNA Fingerprinting

• 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.

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Steps of DNA Fingerprinting

• The pattern of fragment distribution is then analysed.

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Simple Overview

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Uses of DNA Fingerprinting

• Diagnosis of Inherited Disorders

• Developing Cures for Inherited Disorders

• Biological Evidence• Personal Identification

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DNA and Crimes

• Forensic science is the use of scientific knowledge in legal situations.

• The DNA Fingerprint of each individual is highly specific.

• The chances of two people having exactly the same DNA Fingerprint is three million to 1 (except for identical twins).

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DNA Fingerprinting can solve crimes

• The DNA fingerprint pattern is compared with those of the victim and the suspect.

• If matches the suspect, it provides strong evidence that the suspect was present at the crime scene (It does not prove they committed the crime).

• If the DNA fingerprint doesn’t match the suspect then that suspect may be eliminated from the inquiry.

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What kind of crime might DNA fingerprinting provide evidence for?

• A violent murder occurred. • The forensics team retrieved a blood sample

from the crime scene. • Scientists prepare DNA fingerprints of the

blood sample, the victim and two suspects as follows:

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Which suspect was at the crime scene?

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Solving Medical Problems

DNA fingerprints can be used to determine whether a particular person is the parent of a child.

A child's paternity (father) and maternity (mother) can be determined.

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

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Example: A Paternity Test

• By comparing the DNA Fingerprint of a mother and her child it is possible to identify DNA fragments in the child which are absent from the mother and must therefore have been inherited from the biological father.

• Can help us identify health issues from one side of the family.

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Is this man the father of the child?

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Famous cases – the largest child support amount ever awarded

• In 2002 Elizabeth Hurley used DNA profiling to prove that Steve Bing was the father of her child.

• Hurley received $158,000 a month for child support.

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Famous Cases

• Colin Pitchfork was the first criminal caught based on DNA fingerprinting evidence.

• He was arrested in 1986 for the rape and murder of two girls and was sentenced in 1988.

• Caught as a result of mass screenings

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Famous Cases

• O.J. Simpson was acquitted of a double murder charge in 1994 which relied heavily on DNA evidence.

• This case highlighted lab difficulties and the handling of evidence

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