A normal cell, with no mutations, suddenly acquires a mutation in an allele of the RB gene, making it non functional. What would be the phenotype of this cell?

The RB gene is a tumor suppressor gene that plays a crucial role in regulating cell cycle progression. It prevents cells from dividing uncontrollably, which can lead to tumor formation.

When a cell acquires a mutation in an allele of the RB gene that makes it non-functional, the cell loses its ability to regulate cell division effectively. This can lead to uncontrolled cell division, a hallmark of cancer.

However, it's important to note that humans are diploid organisms, meaning they have two copies of each gene (one from each parent). If only one allele of the RB gene is mutated, the other functional allele can still produce the RB protein and regulate the cell cycle. This is why most cancers require two hits (mutations in both alleles) to fully lose function of a tumor suppressor gene.

So, if a cell acquires a mutation in one allele of the RB gene, it may not show any immediate phenotype. However, if the second allele also becomes mutated, the cell would likely start to divide uncontrollably, potentially leading to cancer. This is known as the "two-hit hypothesis".

In summary, a cell with a single mutated RB allele may not show any immediate phenotype, but it is at a higher risk for uncontrolled cell division if the second RB allele also becomes mutated.