Question

R II gene of T${}_4$ phage which is neutral at this locus do not cause lysis of K strain of Escherichia coli. If two strains (R II and rii*) are mixed and then allowed to infect E. coli, it causes lysis. The correct explanation for this is

• A. They belong to same cistron.
• B. They belong to two different cistrons.
• C. They get reverted to the wild.
• D. They get transformed to lytic strains.

Answer 1

Answer: (D)

They get transformed to lytic strains.

A cistron is the functional unit of a gene that exhibits cis-trans complementation test; a gene carries several cistrons. Thus, a cistron codes for a part of the polypeptide and all the cistrons of a gene together make the whole polypeptide. Lysis and lysogeny are determined by different genes, not by part of same genes. Transformation is the transfer of genetic material from one bacterial strain to other without establishing a physical contact. Transformation of a neutral strain to lytic strain is caused by the transfer of genetic material from lytic strain to neutral strain. As mentioned in the question, lysis is caused by mutant strain, r$i{i}^{\ast }$. Thus, the correct answer is option D.