its chromosome = its own chromosome (the bacterium own's chromosome)?

whick = copy?

Context:

The battle between bacteria and bacteria-eating viruses, Wood explains, has been going on for millions of years, with viruses attempting to replicate themselves by -- in one approach -- invading bacteria cells and integrating themselves into the chromosomes of the bacteria. When this happens a bacterium makes a copy of its chromosome, which includes the virus particle. The virus then can choose at a later time to replicate itself, killing the bacterium -- similar to a ticking time bomb, Wood says.