Based upon the cell cycle select the best answer. When Rao and Johnson fused a c

Question

Based upon the cell cycle select the best answer. When Rao and Johnson fused a cell in S phase with a cell in M phase cell they found:

A. mitosis was sped up due to the fact that microtubules donated by the M phase cell were already formed that could attach to the chromosomes from the S phase cell

B. mitosis was unaffected

C. mitosis was delayed because NOT all of the DNA in the M phase cell was fully replicated

D. mitosis was delayed because NOT all of the DNA in the S phase cell was fully replicated

I think it is A or D but I'm not sure.

Explanation / Answer

Rao and Johnson conducted classical experiment in which they tried to fuse two cells in different phases of cell cycle and investigated the effects on the resultant recombinant cell. They took a cell from different phases of cell cycle and fused them with appropriate techniques. However, specifically the fusion product shows reaction in response to the nature of nucleus of the parent cells. This means that the reaction of the resultant recombinant fusion cell will depend upon the nature of the cells and their nuclei which were initially fused.

According to the information, the fusion cells were in S and M phase of cell cycle. The cell in S phase is already replicating its DNA and the cell in M phase is undergoing nuclear division. So, when a fusion is formed, it is highly likely that the rate of mitosis will speed up due to presence of cell-cycle modulating factors released by S-phase nucleus. Since M phase follows after G2 phase, the nucleus from S phase will release factors which will fasten up the process of preparing a cell for division in the M phase. This preparation includes donation of cell-division factors such as cyclin dependent kinases etc along with structural proteins such as microtubular proteins etc.

Thus, this justifies that choice A is correct.

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