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DNA
FINGERPRINTING
Like
the fingerprints that came into use by detectives
and police labs during the 1930s, each person has
a unique DNA fingerprint. 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 between individual
human beings
DNA
Fingerprinting has many uses. It has been used to
solve many disputes involving heredity and criminal
cases. In the SQ006 airplane crash in 2000, genetic
scientists were called in to DNA-fingerprint the genetic
information of victims so authorities could ascertain
their identities quickly. Applications of DNA Fingerprinting
include
-
Diagnosis of Inherited Disorders - Early detection
of such disorders enables the medical staff to prepare
themselves and the parents for proper treatment
of the child
- Developing
Cures for Inherited Disorders - Research programs
to locate inherited disorders on the chromosomes
depend on the information contained in DNA fingerprints.
By studying the DNA fingerprints of relatives who
have a history of some particular disorder, or by
comparing large groups of people with or without
the disorder, it is possible to identify DNA patterns
associated with the disease in question. This work
is a necessary first step in designing an eventual
genetic cure for these disorders
- Biological
Evidence - used to solve many disputes involving
heredity and criminal cases using blood or semen
stains, hair, or items of clothing - found at the
scene of a crime and the suspects
- Personal
Identification - As stated above, DNA fingerprinting
is superior to other methods such as conventional
fingerprints, dental records, etc. It is quite possible
that in future, when you withdraw cash from your
local bank, the cashier might ask for a strand of
hair from you!
Click
here to play a detective game of a modern Sherlock
Holmes where you are asked to solve a murder case
using DNA fingerprinting
Making
DNA Fingerprints
- DNA
fingerprinting is a laboratory procedure that requires
six steps:
- 1:
Isolation of DNA
DNA must be recovered from the cells or tissues
of the body. Only a small amount of tissue - like
blood, hair, or skin - is needed. For example, the
amount of DNA found at the root of one hair is usually
sufficient.
-
2: Cutting, sizing, and sorting
Special enzymes called restriction enzymes are used
to cut the DNA at specific places. For example,
an enzyme called EcoR1, found in bacteria, will
cut DNA only when the sequence GAATTC occurs. The
DNA pieces are sorted according to size by a sieving
technique called electrophoresis. The DNA pieces
are passed through a gel made from seaweed agarose
(a jelly-like product made from seaweed). This technique
is the biotechnology equivalent of screening sand
through progressively finer mesh screens to determine
particle sizes.
- 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.
- 4-5:
Probing.
Adding radioactive or colored probes to the nylon
sheet produces a pattern called the DNA fingerprint.
Each probe typically sticks in only one or two specific
places on the nylon sheet
- 6:
DNA fingerprint.
The final DNA fingerprint is built by using several
probes (5-10 or more) simultaneously. It resembles
the bar codes used by grocery store scanners.
Click
here to see an
animated sequence of the processes involved
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