DNA fingerprinting was developed in 1984 by Alec. J. Jeffrey at
the University of Leicester
He was studying the gene of myoglobin.
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 DNAis determined primarily by the
sequence of letters along the zipper .
Structure of DNA
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. i
Using these sequences, every person could be identified 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:Probing. Adding radioactive or colored probes to the nylon
sheet produces a pattern called the DNA fingerprint.
5: DNA fingerprint.
The final DNA fingerprint is built by using several probes
(5-10 or more) Continuously.
Practical Applications of DNA Fingerprinting
1.Paternity and Maternity
Person inherits his or her VNTRs from his or her parents
Parent-child VNTR pattern analysis has been used to solve
standard father-identification cases.
The primary method of assessing similarities is by use of DNA
fingerprinting or DNA restriction analysis.
This process makes use of special proteins called restriction
enzymes and sections of the chromosome called tandem repeats.
2. Criminal Identification
DNA isolated from blood, hair, skin cells, or other genetic
evidence left at the scene of a crime can be compared
3. Personal Identification
The notion of using DNA fingerprints as a sort of genetic bar
code to identify individuals has been discussed.
4.Diagnosis of Inherited Disorders
diagnose inherited disorders in both prenatal and newborn
babies
These disorders may include cystic fibrosis, hemophilia, sickle
cell anemia, thalassemia, and many others.
Tandem Repeats
A region of the chromosome that contains multiple copies of a
core DNA sequence that are arranged in a repeating fashion Repeats
act as fillers or spacers between coded sections of DNA.
DNA Profiling
A technique used by scientists to distinguish between
individuals of the same species using only samples of their
DNA
Stages of DNA Profiling
Stage 1 :
Cells are broken down
to release DNA
If only a small amount of DNA is available it can be amplified
using the polymerase chain reaction (PCR)
Stages of DNA Profiling
Step 2:
The DNA is cut into fragments using restriction enzymes .
Each restriction enzyme cuts DNA at a specific base
sequence.
Stages of DNA Profiling
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).
Stages of DNA Profiling
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.
DNA is separated on basis of size.
Stages of DNA Profiling
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.
Stages of DNA Profiling
Stage 4:
The pattern of fragment distribution is then analysed.
Crime
Forensic 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 the same DNA profile is 30,000
million to 1 (except for identical twins).
Biological materials used for DNA profiling
Blood
Hair
Saliva
Semen
Body tissue cells
DNA Profiling can solve crimes
The pattern of the DNA profile is then compared with those of
the victim and the suspect.
If the profile the suspect it provides strong evidence that the
suspect was present at the crime scene.
If the profile do not match the suspect then that suspect may
be eliminated from the enquiry.
Example
A 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
References
Molecular Cell Biology By Heavy F.Lodish, Arnold Berk.
DNA Fingerprinting an introduction By Sergio D.J Pena.
Principle of Biochemistry By Leincher.
DNA Fingerprinting and Profiling By Jorg T.Epplen.
