If a cell in metaphase of mitosis is fused with a cell in the G$$_1$$ phase of the cell cycle, the second nucleus will also begin mitosis. What is the most likely explanation for this behavior?

A. Since mitosis takes up most of the time in the cell cycle, it will dominate the newly created fused cell

B. Spindle fibers from the first mitotic cell cannot distinguish between the chromosomes of the two nuclei

C. Molecules such as cyclins are in high concentration in the cytoplasm of a dividing cell and will signal the fused cells nucleus to undergo mitosis

D. The cell senses that it has too high of a surface area to volume ratio following fusion and begins division

C. Molecules such as cyclins are in high concentration in the cytoplasm of a dividing cell and will signal the fused cells nucleus to undergo mitosis

Explanation:

Various stages of the cell cycle are under tight regulation. Specific proteins such as cyclins and cyclin-dependent protein kinases determine if the cell would progress from one stage of the cell cycle to the next. When a cell is in the metaphase, the cyclins specific for mitosis are present in a higher amount in the cell. These cyclins bind to the specific CDKs and activate them.

The activated CDKs then phosphorylate proteins that make the cell to move through various stages of mitosis. Therefore, fusing a G1 cell with a cell in metaphase of mitosis would trigger mitosis in the G1 cell due to the presence of mitosis specific cyclins in the second cell.