The lymphocytes from the blood of the patient are grown in culture in vitro.
A functional ADA cDNA is introduced into lymphocytes using a retroviral vector.
The lymphocytes are introduced back into the blood of the patient.
But a patient requires periodic infusion of such genetically-engineered lymphocytes, as lymphocytes have a life span.
If the functional gene (producing ADA) isolated from marrow cells is introduced into the cells of early embryonic stages, it could be a permanent cure.

A single-stranded DNA or RNA is tagged with a radioactive molecule and used as a probe.
It is allowed to hybridise with its complementary DNA in a clone of cells, followed by detection using autoradiography.
The clone having the mutant gene will not appear on the photographic film, because the probe will not be complementary with the mutated gene.

It is the prohormone which needs to be processed before it becomes a fully mature and functional hormone/, insulin.Proinsulin has three polypeptide chains (A, B and C), whereas insulin has only two (A and B) polypeptide chains.

RNA interference is a gene-silencing process that blocks the expression of genes in the parasite when it enters the host's body.

It is because spores of Bacillus thuringiensis produce the insecticidal Cry proteins that are toxic when ingested by certain insects.

\(\alpha \) -1-antitrypsin is produced to treat emphysema.
The gene for this protein is isolated or synthesized and introduced into a mouse.
The transgenic mouse produces the protein, which is to be isolated, purified and used on human beings after clinical trials.

stem cells are the undifferntiated cells which can divide and differentiate into specialised cells.
They are found in
(i) inner cell mass of blastocyst
(ii) bone marrow
(iii) blood and
(iv) umbilical cord blood.

a) Deletion of the gene for ADA leads to ADA deficiency in the individual.
Since this enzyme is crucial for the immune system to function, it leads to weakening of the immune system.
(b) A functional ADA cDNA is introduced into the lymphocytes of the' patient.
When such lymphocytes are returned to the blood, they are able to synthesise ADA and the disorder is cured.
But it is not a permanent cure; if the functional DNA can be introduced into the cells at early embryonic stages, it becomes a permanent cure.

(i) BT cotton is genetically modified cotton.
(ii) It has been developed by introducing BT toxin gene to the cotton plant from a bacterium which is resistant to bollworms.
(iii) Grandfather was concerned about the well being of his friend and advised him to grow genetically modified, disease resistant variety od frop.

Transgenic animals: Transgenic animals are produced for the following purposes:
(i) Transgenic animals are designed to allow the study of how genes are regulated and how they affect the normal functions of the body and its developments e.g. Information is obtained as to how insulin has a role as growth factor.
(ii) Transgenic animals are designed to increase our understanding as to how genes control the development of diseases; they serve as models for human diseases.
(iii) Transgenic animals that produce useful biological compounds are created by introducing a portion of the DNA that codes for that product, e.g.
\(\alpha \) -L antitrypsin is produced for curing emphysema.
(iv) Transgenic mice are being developed to test the safety of vaccines, e.g., polio vaccine has been tested on mice.
(v) Transgenic animals with more sensitivity to toxic substances are being developed to test the toxicity of drugs.

The bacterium Bacillus thurinqiensis produces proteins, called Bt toxins, which kill the larvae of some insects.
The Bt toxin gene has been isolated and cloned in bacteria.
Such genes are introduced into crop plants, which could be expressed in plants to provide resistance to the insects, i.e. they function as biopesticides; so there is no need for insecticides.
Bt toxins are insect group-specific and coded by cry genes; the proteins encoded by genes crylAc and cryllAb control cotton bollworms while crylAb controls corn borer.
When the insect larvae ingest any plant part, the toxin becomes active in the alkaline pH of the gut and kills  the insect pest. So such plants are resistant to pests.