DNA fingerprinting

Historical backgroundDNA 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 segments that vary in size and composition and have no apparent function are called minisatellites

The different sequences is the same as the word "POST" has a different meaning from "STOP" or "POTS," even though they use the same letters.

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 FingerprintsDNA 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 piecesis 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.

4-6: DNA fingerprint.The final DNA fingerprint is built by using several probes (5-10 or more) simultaneously.

Practical Applications of DNA Fingerprinting

1.Paternity and MaternityPerson inherits his or her VNTRs from his or her parents Parent-child VNTR pattern analysis has been used to solve standard father-identification cases

Example: A Paternity TestBy comparing the DNA profile 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.

Is this man the father of the child?

Mother Child Man

2. Criminal Identification & ForensicsDNA 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

CrimeForensic science is the use of scientific knowledge in legal situations.The DNA profile of each individual is highly specific.The chances of two people having exactlythe same DNA profile is 30,000 million to 1 (except for identical twins).

Biological materials used for DNA profiling

BloodHairSalivaSemenBody tissue cells

DNA Profiling can solve crimesThe pattern of the DNA profile is then compared with those of the victim and the suspect.If the profile matches the suspect it provides strong evidence that the suspect was present at the crime scene (NB: it does not prove they committed the crime).If the profile doesn’t match the suspect then that suspect may be eliminated from the enquiry.

ExampleA violent murder occurred. The forensics team retrieved a blood sample from the crime scene. They prepared DNA profiles of the blood sample, the victim and a suspect as follows:

Was the suspect at the crime scene?

Suspects Profile

Blood sample from crime scene

Victims profile

3. Personal IdentificationThe notion of using DNA fingerprints as a sort of genetic bar code to identify individuals

4. Diagnosis of Inherited Disordersdiagnose inherited disorders in both prenataland newborn babiesThese disorders may include cystic fibrosis, hemophilia, Huntington's disease, familial Alzheimer's, sickle cell anemia, thalassemia, and many others.

5.Developing Cures for Inherited Disorders

By studying the DNA fingerprints of relatives who have a history of some particular disorderidentify DNA patterns associated with the disease