DNA Fingerprinting
DNA fingerprinting is the method of identifying DNAs
of different persons by locating differences in the
arrangement of nucleotides in those specific regions in
DNA sequence, which are repeated several times. This
technique was invented in 1977 by a British geneticist,
Sir Alec Jeffreys at Leicester University.
Procedure of DNA Fingerprinting
Step I. Isolation of DNA DNA must be re cov ered
from the cells or tis sues of the body. Only a
small amount of tis sue like blood, sa liva,
se men, hair or skin is re quired as source.
Step II. Cutting, sizing and sorting Spe cial en zymes
called re stric tion en zymes are used to cut the
DNA at spe cific places. The DNA pieces are
sorted ac cord ing to size by a siev ing
tech nique called elec tro pho re sis. The DNA
pieces are passed through a gel made from
sea weed agarose.
Step III.Transfer of DNA to nylon The dis tri bu tion of
DNA pieces is trans ferred to a ny lon sheet by
plac ing the sheet on the gel and soak ing them
over night. The pro cess be ing called as
south ern hy bridi sa tion.
Step IV.Probing Add ing ra dio ac tive or col oured
probes to the ny lon sheet pro duces a pat tern
called the DNA fin ger print. Each probe
typ i cally sticks in only one or two spe cific
places on the ny lon sheet.
Step V. DNA fingerprint The fi nal DNA fin ger print is
built by us ing sev eral probes (5-10 or more)
si mul ta neously. The seg ments marked with
probes are ex posed on X-ray film, where they
form a char ac ter is tic pat tern of black bars − the
DNA fingerprint.
Ap pli ca tions of DNA Fin ger print ing
(i)Fo ren sic uses In crim i nal in ves ti ga tions, DNA from sam ples of
hair, body flu ids or skin at a crime scene is com pared with
those ob tained from sus pected per pe tra tors. DNA typ ing is
also used to iden tify the re mains of un known in di vid u als, as in
the iden ti fi ca tion of the sol diers or to iden tify the
un re cog nis able bod ies of peo ple killed in po lit i cal vi o lence or
ac ci dents whose bod ies are
(ii)Pa ter nity Pa ter nity de ter mi na tion is pos si ble with DNA typ ing
be cause half of the fa ther’s DNA is con tained in the child’s
ge netic ma te rial.
(iii)An thro pol ogy DNA fin ger print ing has also been used
ex ten sively to iden tify hu man re mains, solv ing long-stand ing
mys ter ies. DNA has had an enor mous im pact on an thro pol ogy
as well.
(iv)Wild life man age ment The more the ge netic makeup of
nat u ral pop u la tions is un der stood, the better con ser va tion and
man age ment plans will be executed.Mobile Genetic Elements of Genome
Transposons are special small fragments of DNA (700 to 40,000 base pairs
long) that can move from one region of DNA molecule to another. These are
also called ‘jumping genes’. These jumping genes were discovered by Barbara
McClintock (1950s) in corn. These occur in all organisms and have been
studied most thoroughly in microorganisms. All transposons contain the
information for their own transposition. For example, the simplest transposons
(also called insertion sequences) contain only a gene that codes for an enzyme
transposase (catalyses the cutting and resealing of DNA during
transposition) along with recognition sites (short, inverted, repeat sequences
of DNA for enzyme recognition between transposons and rest DNA).
Transposons with antibiotic resistance genes are of practical interest, but
there is no limitation on the kinds of genes which transposons can have. Now,
we can say that transposons provide a natural mechanism for movement of
genes from one chromosome to another and as these may be carried between
cells or plasmids or viruses they can also spread from one organism to another
or from one species to another. Thus, today transposons are considered as a
potentially powerful mediator of evolution in organisms.CBSE CHAPTERWISE
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