Download What is Genetic Modification?

GENETICALLY MODIFIED CROPS
Dr VISHAL SHARMA
Assoc. Proff
Government Post Graduate College For Girls-11,Chandigarh
What is Genetic Modification?
Genetic modification involves altering an organism's DNA.This
can be done byaltering an existing section of DNA, or by adding
a new gene altogether.A gene is a code that governs how we
appear and what characteristics we have.Like animals, plants
have genes too. Genes decide the colour of flowers, and
how tall a plant can grow. Like people, the characteristics of a
plant will be transferred to its childrenthe plant seeds, which
grow into new plants
How does a genetic scientist work?
Genetic modification of plants occurs in several stages:
1. An organism that has the desired characteristic is identified.
2. The specific gene that produces this characteristic is located and cut out
of theplant’s DNA.
3 To get the gene into the cells of the plant being modified, the gene needs
to beattached to a carrier. A piece of bacterial DNA called a plasmid is
joined to thegene to act as the carrier.
4. A type of switch, called a ‘promoter’, is also included with the combined gene and carrier. This helps make sure the gene works properly when it
is put into the plant being modified. Only a small number of cells in the
plant being modified will actually take up the new gene. To find out which
ones have done so, the carrier package often also includes a marker gene
to identify them.
5. The gene package is then inserted back into the bacterium, which is allowed to
reproduce to create many copies of the gene package.
6. The gene packages are then transferred into the plant being modified. This is
usually done in one of two ways:
By
attaching the gene packages to tiny particles of gold or tungsten and
firing them at high speed into the plant tissue. Gold or tungsten are used
because they are chemically inert – in other words, they won't react with
their surroundings
By
using a soil bacterium, called Agrobacterium tumefaciens, to take it in
when it infects the plant tissue.
Golden rice
Golden rice is genetically modified rice that now contains a large amount of A-vitamins. Or more
correctly, the rice contains the element beta-carotene which is converted in the body into
Vitamin-A. So when you eat golden rice, you get more vitamin A.
Beta-carotene gives carrots their orange colour and is the reason why genetically modified rice
is golden. For the golden rice to make beta-carotene three new genes are implanted: two from
daffodils and the third from a bacterium.
Advantages:
•The rice can be considered a particular advantage to poor people in underdeveloped
countries. They eat only an extremely limited diet lacking in the essential bodily vitamins.
The consequences of this restricted diet causes many people to die or become blind.
This is particularly true in areas of Asia, where most of the population live on rice from
morning to evening.
Disadvantages:
•Critics fear that poor people in underdeveloped countries are becoming too dependent
on the rich western world. Usually, it is the large private companies in the West that have
the means to develop genetically modified plants. By making the plants sterile these
large companies can prevent farmers from growing plant-seed for the following year forcing them to buy new rice from the companies.
Some opposers of genetic modification see the "golden rice" as a method of making
genetic engineering more widely accepted. Opponents fear that companies will go on
to develop other genetically modified plants from which they can make a profit. A
situation could develop where the large companies own the rights to all the good crops
FLAVR SAVR™ tomatoes were developed using recombinant DNA techniques to express
the trait of delayed softening of tomato fruit. The novel variety was developed by
insertion of an additional copy of the polygalacturonase (PG) encoding gene in the
“antisense” orientation, resulting in reduced translation of the endogenous PG
messenger RNA (mRNA). The antisense PG gene is essentially a reverse copy of part of
the native tomato PG gene that suppresses the expression of endogenous PG enzyme
prior to the onset of fruit ripening. The mechanism of decreased PG activity in FLAVR
SAVR™ tomato is likely linked to the hybridization of antisense and sense mRNA
transcripts, resulting in a decreased amount of free positive sense mRNA available for
protein translation. Reduced PG expression decreases the breakdown of pectin and leads
to fruit with slowed cell wall breakdown, better viscosity characteristics and delayed
softening. FLAVR SAVR™ tomatoes have improved harvest and processing properties that
allow the transgenic tomatoes to remain longer on the vine to develop their natural
flavour, maintain firmness for shipping and produce a thicker consistency in processing.
Modification Method
This bioengineered tomato was produced by Agrobacterium-mediated
transformation of tomato (Lycopersicon esculentum) in which the transfer-DNA (TDNA) region of the bacterial tumour inducing (Ti) plasmid was modified to contain
DNA sequences encoding an “antisense” PG gene construct and the NPTII encoding
neo gene from E. coli K12. During transformation, the T-DNA portion of the plasmid
was transferred into the plant cells and stably integrated into the plant's genome.
The antisense PG gene was under the regulatory control of a single copy of the 35S
promoter from the cauliflower mosaic virus (CaMV), or two tandem copies of the
35S promoter. The terminator sequences were from the tml gene and the
transcript 7 gene from the octopine-type Ti plasmid pTiA6 from A. tumefaciens.
Expression of the neo gene was under the control of the 5' promoter and 3'
terminator sequences from the mannopine synthase gene derived from A.
tumefaciens.