valuable proteins have been transferred into
rabbits, interleukin 2, growth hormone, tissue
plasminogen activator, a 1 antitrypsin, etc. These
genes are expressed in mammary tissues and
proteins were harvested from milk.
(ii) Transgenic animals are being made that carry
genes which make them more sensitive to toxic
substances than non-transgenic animals. They
are then exposed to the toxic substances and the
effects are studied. Transgenic mice is used as
model for studying techniques of gene transfer
and transgenic production.(c) Diagrammatic representation of synthesis of cDNA
from RNA is as follows:
mRNA
cDNAmRNA
Reverse transcriptaseTreat with alkali to
digest mRNADouble-stranded
cDNAComplementary
DNA made (cDNA)Single-stranded
complementary DNADNA polymerase makes
complementary DNA strand- (a) PCR (Polymerase Chain Reaction) is used to detect
mutations in gene in suspected cancer patients.
A single stranded DNA or RNA joined with a
radioactive molecule (probe) is allowed to hybridise
to its complementary DNA in a clone of cells. It is
followed by detection using autoradiography. The
clones having the mutated gene will not appear on
the photographic film, because the probe will not
have the complementarity with the mutated gene.
(b) The three methods which force ‘alien’ or recombinant
DNA into host cells are: electroporation, biolistic
method and microinjection.
(i) Electroporation : In this method, electrical impulses
induce transient pores in the cell membrane of host cells
by using lysozyme or calcium chloride through which
foreign DNA molecules are incorporated into cells.
(ii) Biolistic method or Gene gun method : Biolistic
is a means of introducing DNA into cells that
involves bombardment of cells with high-velocity
microprojectiles coated with DNA. In biolistic method
tungsten or gold particles, coated with foreign DNA
are bombarded into target cells at a very high velocity.
(iii) Microinjection : It is the introduction of foreign gene
into nucleus of plant cell or animal cell by using
microneedles or micropipettes. It is used in oocyte, egg
or embryo.
Microinjection needle
containing foreign DNACytoplasm
NucleusSuctionHolding pipette
Host cell
OR
(a) GM plants have been useful in many ways :
(i) Growing GM crops can help to reduce the use of
chemical pesticides, e.g., Bt cotton.
(ii) GM crops are more tolerant to abiotic stresses (cold,
drought, salt, heat, etc.).
(iii) They have helped to reduce post-harvest losses, e.g.,
Flavr savr transgenic tomato.
(iv) Increased efficiency of mineral usage by plants prevents
early exhaustion of fertility of soil.
(v) GM plants enhance nutritional value of food. E.g.,
vitamin A enriched rice.
(vi) GM plants are resistant to herbicides.
(vii) Plants such as popular trees have been genetically
engineered to clean up heavy metal pollution from
contaminated soil.
GM food can lead the following health problems.
(i) Allergies : The transgenic food may be cause toxicity
and or produce allergies. The enzyme produced by the
antibiotic resistance gene can cause allergies, because
it is a foreign protein.
(ii) Effect on bacteria of alimentary canal : The bacteria
present in the human alimentary canal can take up
the antibiotic resistance gene that is present in the
GM food. These bacteria can become resistant to the
concerned antibiotic and will be difficult to manage.
(b) GEAC is Genetic Engineering Approval Committee. It
makes decisions regarding the validity of GM research
and the safety of introducing GM organisms for public
services. The objectives of setting up GEAC by our
government are as follows:
(i) To permit the use of GM organisms and their products
for commercial applications.
(ii) To adopt procedures for restriction, production, import,
export and application of GM organisms.
(iii) To approve for conduct of large scale field trials and
release of transgenic crops in the environment.
(iv) To authorise agencies or persons to have large scale
production and release of GM organisms into the
environment or curb and take punitive action against
them.