Scientists can create transgenic organisms by inserting foreign DNA randomly into the chromosomes of a host. A scientist might do this in order to express genes carried in the foreign DNA and in this case the foreign DNA is often engineered to include insulator sequences at the ends of the foreign sequence. Why insulators would be useful in this context

Insulator sequences serve as a boundary between two genes. In this case, the insulator sequence is a boundary between the organism's normal DNA and the inserted foreign DNA. The insulator will protect the inserted DNA from any regulatory effects that may come from the neighboring gene.

the cell cycle is the final answer! : )

as in mitosis, dna replication occurs during interphase.   in meiosis, it occurs specifically in s phase of interphase 1.