Which option gives the correct source of T4 DNA ligase?

Correct answer: T4 bacteriophage

The governing concept is the source and nomenclature of enzymes used in recombinant-DNA technology. T4 DNA ligase is obtained from bacteriophage T4, so option A is correct. The designation “T4” identifies the bacteriophage associated with the enzyme; it does not refer to a plant, human tissue, or fungus. T4 DNA ligase joins compatible DNA ends by catalysing formation of phosphodiester bonds in the DNA backbone, using ATP as an energy source. This activity makes it useful for ligation of an insert into a vector during cloning. Mango leaf, human bone, and fungal cap are not the standard biological sources indicated by the enzyme’s name and therefore are implausible distractors.