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Functional adenosine is given to the patient by injection.

Disadvantages : 

Therapy is not completely curative periodic infusion of enzyme required.

Detailed Answer : 

Adenosine deaminase deficiency is a genetic disorder. The disorder is caused due to the deletion of the gene for adenosine deaminase, the enzyme crucial for the immune system to function. 

Adenosine deaminase deficiency in patients can be treated by enzyme replacement therapy. In this treatment, patients are regularly injected with the functional ADA enzyme. 

Disadvantages of this Process : 

(a) It does not completely eradicate the disease. 

(b) The requirement of repeated doses of the enzymes makes it expensive.

As this therapy does not cure the disease completely it requires periodic treatment.

Detailed Answer :

They need periodic treatment because it is not a completely curative method. In this method, a functional ADA-cDNA is infected into a patient, by introducing it into patient's lymphocytes using a retroviral vector-since lymphocytes have a definite life cycle, there is a need for periodic infusion of genetically engineered lymphocytes (having ADA) into the patient.

The above statement can be substantiated through DNA finger printing by southern blot method and by PCR. 

DNA from all the cells of an individual shows the same degree of polymorphism. 

The polymorphs are heritable. An individual and inherits 50% of the chromosomes from maternal and 50% from the paternal parent. Small amount of DNA from blood or tissue is taken and amplified by PCR, which can be used in DNA finger printing so as to identify the paternity.

Two chains of DNA sequence corresponding to A and B chains of human insulin prepared, introduced them into plasmids of E. coli to produce separate A and B chains, A and B chains extracted combined by creating disulphide bonds.

Detailed Answer : 

American Company Eli Lilly used the knowledge of r-DNA technology to produce human insulin in the following way. 

1. Preparation of DNA corresponding to A and B chain separately. 

2. Extraction of plasmid from bacteria. 

3. Insertion of DNA corresponding to A and B chain separately in plasmid. 

4. Transforming the bacteria with this recombinant plasmid. 

5. Expression of the desired product from this DNA . 

6. Purication of A and B chain. 

7. Linking them with disulde bonds so that they act as human insulin.

(i) Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton. The choice of genes depends upon the crop and the targeted Pest, as most Bt toxins are insect-group specific. 

(ii) The toxin is coded by a gene named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton ballworms, and that of cryIAb controls corn borer.

Produce Proinsulin chain A and chain B using separate DNA sequences introduced in the plasmids of E.coli, extracted, combined by disulphide bond produces mature insulin. 

Insulin produced by human Pancreas has an additional C peptide.

 (i) The Ti plasmid (tumor-inducing plasmid) of Agrobacterium tumefaciens has been modified (does not cause tumour) and used as a cloning vector. The Ti plasmid integrates a segment of its DNA, termed T-DNA, into the chromosomal DNA of its host plant cells. 

(ii) The T-DNA plasmid causes tumours. As gene transfer occurs without human effort, the bacterium is known as 'natural genetic engineer' of plants. Ti plasmids as vectors transfer foreign genes of interest into the target cells.

An extra-chromosomal DNA which delivers gene of interest into variety of plants and act as cloning vector is called Ti plasmid. They are present in Agrobacterium tumifaciens. Ti plasmid vectors are used for genetic transformation in many dicot plants. The tumour inducing (Ti) plasmid of Agrobacterium tumifaciens has been modified into a cloning vector which is no more pathogenic to the plants but is still able to use the mechanisms to deliver genes of interest into a variety of plants.

The recombinant/transformant may be found out from non-recombinant/non-transformant by plating the transformants on ampicillin containing medium. The transformants growing on ampicillin containing medium are then transferred to tetracycline containing medium. The recombinant will grow on ampicillin containing medium but not on that containing tetracycline. But non-recombinant will grow on both tetracycline and ampicillin containing media.

a. EcoRI is a restriction endonuclease, obtained from an E. coli bacterium. R represents the name of the strain.

b. It cuts the DNA between bases G and A on both the strands only when the sequence GAATTC is present in DNA.

i. Escherichia coli.

ii. Origin of replication or ‘ori’ controls copy number of inserted gene.

iii. The selectable markers are amp^R and tet^R (resistance to ampicillin, tetracycline). Selectable markers help to select the host cells which contain the vector (transformants) and eliminate non-transformants. If a foreign DNA ligates at the BamHI site of tetracycline resistance gene in the vector pBR322, the recombinant plasmid loses the tetracycline resistance due to insertion of DNA. It can still be selected out from non-recombinant.