Gene Transfer Technologies

• (i) COSMIDS:
  • Can carry large DNA inserts (up to 45 kb).
  • Contain cos sites from bacteriophage lambda for packaging into phage particles.
  • Have bacterial origin of replication and antibiotic resistance marker for selection.
• (ii) Shuttle Vectors:
  • Contain origins of replication for two different host species (e.g., E. coli and yeast).
  • Allow replication and selection in multiple host organisms.
  • Include selectable marker genes for both hosts.
• (iii) Expression Vectors:
  • Contain strong promoter sequences for high-level expression of cloned genes.
  • Have regulatory elements like operator sequences and ribosome binding sites.
  • Include selectable markers and multiple cloning sites.
  • Often possess tags (e.g., His-tag) to facilitate purification of expressed proteins.

Adenosine deaminase (ADA) is an enzyme involved in purine metabolism. Its absence leads to the accumulation of toxic metabolites that severely affect the immune system, causing Severe Combined Immunodeficiency (SCID), a genetic disorder characterized by a weakened immune response.

• SCID: Caused by ADA deficiency, leading to impaired immune function.
• Thalassemia and Sickle cell anaemia: Are blood disorders caused by mutations in hemoglobin genes, unrelated to ADA.
• Mad cow disease: Is a prion disease affecting the brain, unrelated to ADA enzyme.

Thus, the correct answer is (C) SCID.

M13 bacteriophage based vectors are filamentous phages used in molecular cloning to produce single-stranded DNA. This property makes them ideal for applications like DNA sequencing or site-directed mutagenesis where single-stranded DNA is required.

• M13 based vector: Produces single-stranded DNA, suitable for gene sequencing.
• Lambda bacteriophage vector: Typically produces double-stranded DNA.
• Plasmid vectors (pUC family, pBR 322): Circular double-stranded DNA vectors used for cloning but do not generate single-stranded DNA naturally.

Hence, the correct choice is (A) M13 based vector.