During which stage of the cell cycle do two new nuclei form?

I believe the correct answer is Mitosis.

The cell cycle has 4 stages with one resting stage. In the Third stage called Mitosis the nucleus is divided into 2 daughter nuclei and the cell starts to undergo cytoplasmic division.

It is the first phase of the cell cycle and the cell is undergoing recovery fro its previous cellular division. It starts to double its organelles and accumulates raw materials that will be used for DNA synthesis in the next phase. In this stage also, the DNA is checked for any abnormalities or damages and if any is found, the cell undergoes a programmed cell death called apoptosis. It takes 11 hours to complete.

b) Synthesis (S) Phase:

This is a phase where DNA synthesis/replication occurs. Chromosomes usually enter the S phase with one chromosome but move on to the next phase with 2 identical chromosomes. It takes up to 8 hours.

c) Gap 2 (G2) Phase:

It is the third phase and is between the Mitotic phase and the synthesis phase. The cell synthesizes all the proteins that are required for cell division to occur. The cell is also checked for DNA abnormalities and if any are found, the cell undergoes apoptosis. It takes 4 hours for this process to complete.

d) Mitosis (M) Phase:

It is the last phase of the cell cycle and there it is in this phase that the nucleus divides. It is a lengthy process. Chromatins are condensed and the chromatids are attached at the centromere. The nuclear envelope disintegrates and the nucleolus disappears. Spindle fibers begin to take shape and two centrosomes move away from each other at the center forming microtubules in star-like arrays. Centromere of each chromosome develops 2 kinetochores. Chromosomes are pulled around by kinetochore fibers and forced to align across equatorial plane of cell. Centromere dissolves releasing sister chromatids and the sister chromatids separate. The spindle fibers then disappear and two clusters of daughter chromosomes formed forming daughter nuclei. Nuclear envelopes form around the two incipient daughter nuclei, chromosomes uncoil and become diffuse chromatin again. Finally, the nucleolus reappears in each daughter nucleus.

Also important to note is the G0 phase where the cell undergoes resting and there is totally no activity taking place. Many cancerous cells optimize this phase by avoiding it and going directly to the synthesis stage hence no DNA abnormalities are checked.

Level : High School