A particular cell type spends 4 hours in G1 phase, 2 hours in S phase, 2 hours in G2 phase, and 30 minutes in M phase. If a pulse-chase experiment was performed with radioactive thymidine on an asynchronous culture of such cells, what percentage of mitotic cells would be radiolabeled 9 hours after the pulse

Explanation:

1. As given, cell cycle is of 8.30 hours.

G1 phase= 4 hours;

S phase= 2 hours;

G2 phase = 2 hours;

M phase= 30 minutes.

2. Adding up each phase shows that the cell cycle is 8.5 hours long. As after 9 hours, the radio labeled cells would have passed through a full cycle ( from G-1 to m phase) and be in either S phase or G2- phase and  none cell  would have entered M Phase.

3. DNA  synthesis occurs only in S-phase, so the incorporation of any radioactive nucleotide happens in S-phase only.

4. M phase, cell divide itself into two daughter cells.

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