Final answer:
The cI gene in the lambda phage encodes for the cI repressor protein, which promotes the lysogenic cycle by inhibiting the expression of lytic genes; an inactive cI can lead to the transition to the lytic cycle.
Step-by-step explanation:
The function of the cI gene in the lambda phage is crucial for determining the life cycle of the phage after it infects a bacterial host. The cI protein, produced by this gene, is a repressor that can bind to the phage’s DNA and inhibit the expression of genes necessary for the lytic cycle. When the cI protein is present and active, it promotes the lysogenic cycle, where the phage’s DNA integrates into the bacterial host's chromosome and replicates along with it without causing immediate harm to the host.
However, when the cI protein is inactive or its levels decrease, the phage can switch to the lytic cycle, leading to the production of new phage particles and the eventual lysis of the host cell. In summary, the cI gene plays a central role in maintaining the balance between the lytic and lysogenic pathways within an infected bacterial cell.