How many fragments will be generated, if a linear DNA molecule is digested with a restriction enzyme having 4 recognition sites on the DNA?

5

The correct answer is Option (2)-5

If a linear DNA molecule is digested with a restriction enzyme having 4 recognition sites on the DNA, it will generate 5 fragments.

When a restriction enzyme cuts a linear DNA molecule at its recognition site, it creates two ends on each side of the site. Since there are 4 recognition sites, there will be 4 cuts, resulting in 5 fragments: one fragment on the left end, three fragments between the recognition sites, and one fragment on the right end.

If DNA is linear then the number of fragments generated is (N+1), where N= number of recognition sites or sequences. 

Hence the number of fragments generated is 5 if we digest a linear DNA molecule with a restriction enzyme having four recognition sites on the DNA.