Final answer:
When a bacteriophage genome is incorporated into the chromosome of the host bacteria, it is known as a prophage. This usually occurs during the lysogenic cycle, where the prophage can remain latent until specific environmental triggers induce a return to the lytic cycle.
Step-by-step explanation:
When a bacteriophage genome incorporates itself into the chromosome of the host, that phage genome is referred to as a prophage. During the lysogenic cycle, a temperate bacteriophage such as the lambda phage injects its DNA into the bacterial host, where it may integrate into the bacterial chromosome instead of immediately causing cell death through the lytic cycle. The bacterium carrying the integrated prophage is known as a lysogen.
This prophage replicates along with the host cell's DNA, potentially passing on new characteristics, in a process called lysogenic conversion or phage conversion, until certain environmental stressors trigger its excision and return to the lytic cycle.