Question

Following are the steps in one type of gene therapy.
i. Inject engineered cells into patients’ bone marrow.
ii. Viral DNA earring the normal allele inserts into the chromosome.
iii. Let retrovirus infect bone marrow cells that were removed from the patient and cultured.
iv. Insert RNA version of normal allele into a retrovirus.
The correct sequence is:
A. (i), (ii), (iii) and (iv)                     
B. (iv), (iii), (ii) and (i)
C. (i), (ii), (iv) and (iii)                     
D. (iv), (iii), (i) and (ii)

Answer 1

Hint: Gene therapy is a method that changes a person's genes to cure or treat disease. Gene therapies can be operated by various mechanisms: Substituting a disease-causing gene with a healthy copy of the gene. Disarming a disease-causing gene that doesn't work properly.

Complete Step-by-step answer:

Retroviral vector-mediated gene transfer was central to the evolution of gene therapy. Retroviruses have multiple different advantages over other vectors, particularly when permanent gene transfer is the preferred outcome. The most significant benefit that retroviral vectors offer is their capacity to transform their single-stranded RNA genome into a double-stranded DNA molecule that stably incorporates into the target cell genome.
This means that retroviral vectors can be utilised to permanently change the host cell’s nuclear genome. 
Generally, a retrovirus is utilised as a vector for introducing a DNA fragment into human cells. They are utilised as vectors in gene therapy to introduce the desired gene so as to substitute the functioning of the desired gene to substitute the functioning of a defected gene e.g. Severe Combined Immune Deficiency (SCID) is caused because of a defect in the gene for the enzyme adenosine deaminase. In gene therapy against it, lymphocytes are extracted from the bone marrow of the patient. These are grown in a culture outside the body. Using a retroviral vector, a functional ADAs cDNA, is then introduced into these lymphocytes. These are reinjected into the patient's bone marrow.
Therefore the correct answer is Option B.

Note: Retrovirus is being used as a vector for human lymphocytes. λ phage is being used for bacteria. Ti plasmid is used for DNA transfer in plants. pBR 322 is a plasmid vector usually used in bacterial transformations.