Which of the following statements are false?

1. Transposition occurs by non-replicative mechanism only.
2. Homologous recombination between multiple copies of a transposon causes rearrangement of host DNA.
3. Homologous recombination between the repeats of transposons may lead to precise or imprecise excision.
4. Imprecise excision describes the removal of a transposon plus one of the duplicated target sequences from the chromosome.

Correct answer. Transposition occurs by both replicative and non-replicative mechanisms. All transposons use a common mechanism in which staggered nicks are made in target DNA, the transposon is joined to the protruding ends, and the gaps are filled. The order of events and exact nature of the connections between transposon and target DNA determine whether transposition is replicative or nonreplicative. Precise excision describes the removal of a transposon plus one of the duplicated target sequences from the chromosome. Imprecise excision occurs when the transposon removes itself from the original insertion site, but leaves behind some of its sequence.