Q.The following events occur during the various phases of the cell cycle, Name the phase against each of the events.
a. Disintegration of nuclear membrane ______
b. Appearance of nucleolus ______
c. Division of centromere ______
d. Replication of DNA ______

Each of these four events belongs to a specific, identifiable stage of the cell cycle, following the normal progression from interphase through mitosis.

• a. Disintegration of the nuclear membrane — Prophase, by the end of which the nuclear envelope (along with the Golgi complex, ER and nucleolus) has completely broken down.
• b. Appearance (reappearance) of the nucleolus — Telophase, when the nucleolus reappears as the nuclear packaging changes of mitosis are reversed. …

Going through each event against the stage where it is specifically described:

• a. Disintegration of the nuclear membrane. By the end of prophase, the chromosomal material has already condensed into compact mitotic chromosomes, and the Golgi complex, endoplasmic reticulum, nucleolus and the nuclear envelope all disintegrate — this breakdown of the nuclear envelope is the defining event that closes out prophase and frees the chromosomes so spindle fibres arriving from the cytoplasm can reach and attach to their kinetochores.
• b. Appearance of the nucleolus. This happens at telophase, the last stage of karyokinesis, which essentially reverses the packaging changes of earlier mitosis. As the nuclear envelope re-forms around each cluster of chromatin, the nucleolus reappears, along with the Golgi complex and endoplasmic reticulum.
• c. Division of the centromere. This is the defining event of anaphase, which begins with the simultaneous splitting of the centromere of every chromosome — since the centromere was what held the sister chromatids together, its division is what allows them to be pulled apart toward opposite poles. …

Step 1 — For each listed event, recall the mitotic stage where the chapter specifically places it.

Step 2 — a. Nuclear envelope breakdown is described as completing by the END of prophase (together with the Golgi complex, ER and nucleolus disappearing) — so the answer is Prophase, not metaphase (metaphase only begins once this breakdown is already complete). …