Class 12th Biology 2012 Set3 Delhi Board Paper Solution

(a) DNA ligase enzyme is used to join two DNA fragments from their ends.

(b) When Meloidogyne incognita (parasite) consumes cells with RNAi gene, parasite cannot survive and this prevents infestation. The introduced RNAi gene DNA forms both sense and anti-sense RNA. Two strands being complementary to each other bend and form ds RNA, leading to RNAi. Thus, the mRNA of nematode is silenced and the parasite cannot survive there.