It is a therapy in which germ cells i.e., sperms or eggs (even zygotes) are modified by the introduction of functional genes which are ordinarily integrated into their genomes. Therefore, the change due to therapy is heritable and passed on to later generations.

Gene probe is a radioactively labelled cloned section of DNA that is used to detect identical sections of nucleic acid by means of pairing between complementary bases. In Southern blotting, DNA segments are diagnosed. In Northern blotting. RNA is identified.

Genetic disease is caused by unproper functioning of some gene which results in non functioning of enzymes, non formation or wrong formation of proteins and other biochemicals. Therefore, genetic diseases cannot be treated by methods used in infections like killing of pathogens and strengthening of immune system.

Rosie is the first transgenic cow.
The milk contained human protein, \(\alpha\) -lactalbumin (2.4 g per litre) which is nutritionally important for human babies.

A hereditary disease can be corrected by gene therapy, which is a collection of methods that allows correction or replacement of a defective gene.
Correction of a genetic defect involves the delivery of a normal gene in the individual at the embryonic stage; this is to make the delivered/introduced  gene to take the function of the defective, gene.
ADA-deficiency has been corrected by gene therapy.

The toxoids are a kind of vaccine which is prepared by detoxication of the toxins produced by pathogenic microbes

Potential applications of genetically modified plants are:
(i) nutritional enhancement, e.g vitamin-A enriched rice.
(ii) Stress tolerance crops are more toleeant to abiotic stresses such as cold, drought, etc.
(iii) Creation of tailor made plants by using GM plants to supply alternative resources to industries in the form of starches, biofuels, etc.

Very low concentration of a bacteria or virus in human body can be detected by amplification of their nucleic acid using the technique of polymerase chain reaction (PCR).This method is applied to detect HIV in suspected AIDS patients and to detect mutations in genes in suspected cancer patients.

Cry proteins are the crystal proteins that are toxic to certain insect pests (Dipterans, Coleopterans and Lepidopterans).
They are produced by the bacterium Bacillus thuringiensis .
Man has isolated the genes encoding these proteins from this bacterium and incorporated into some crop plants; such crop plants produce the proteins in their cells and are resistant to the attack by these insect pests.

Bacteria that have had their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic bacteria, eg. DNA sequences introduced in plasmid of E. coli to produce insulin chains.

(i) Options to increase food supply:
Agro-chemical based agriculture, using chemical fertilizers and pesticides.
Organic agriculture, using biofertilizers, biopesticides, vermi composting, etc.
Genetically-engineered (GM) crops based agriculture.
(ii) The success of Green Revolution was due to Use of improved/hybrid crop varieties  Better management practices.
Use of agrochemicals (pesticides and fertilisers).
(iii) We still search for other methods for the following reasons:
The agrochemicals cause pollution of soil and water and reduce the yield in the long run; they are too expensive for the farmers. Further increase in the yield of the existing varieties by conventional breeding is not possible.

Bacillus thuringiens· :
(a) This bacterium produces a protein, which is toxic to he larvae of insects like bollworm, budworm, flies, bettles,etc.
 Bt-toxin gene has been cloned from the bacteria and been expressed in plants to provide resistance to insects without the need for chemical insecticides.
(b) The gene (cry) coding for the protein has been isolated using restriction enzymes.
They are cloned in the vectors and then introduced into a number of crop plants like cotton, tomato, corn, rice, etc.
There are a number of different forms of the gene, that code for insect-specific Cry proteins, e.g., crylAc and cryllAb control cotton bollworm.
crylAb controls corn borer.
The transgenic plants (called as Bt corn, Bt rice, Bt cotton, etc.) produce the protein in their cells and express the insect/pest resistance.

Deletion of the gene for ADA causes ADAdeficiency, i.e. deficiency of adenosine deaminase, the enzyme which is crucial for the normal functioning of our immune system.
 ADA deficiency can be cured by:
(i) Bone marrow transplantation.
(ii) Enzyme replacement therapy in which functional ADA is given by injection.
(iii) Gene therapy, in which functional ADA cDNA is introduced into lymphocytes or into cells at early embryonic stage.