Question

Now, suppose that a mammalian cell line is heterozygous at the locus encoding P53. One allele encodes active P53, the other allele harbors a nonsense codon. In one cell, a chromosome breaks because of radiation exposure. What happens for this cell?

It divides on

It gets stuck in M phase (at least for a while)

It gets stuck in G1 (at least for a while)

Answer 1

P53 is a gene which prevents tumor also known as Guardian of the genome.

It can regulate cell cycle if there is DNA damage. It holds the cell cycle at G1 or S phase and activates DNA repair proteins. If the damage is not repaired then p53 initiates program celled death or apoptosis.

Here, the mammalian cell line is heterozygous for p53. Means two locus of that gene are different, one encodes active p53 another codes for nonsense codon. So one allele will produce the p53 protein . The allele with nonsense codon can not produce the protein.

If, in one cell chromosome breaks due to radiation exposure, the cell will gets stuck in G1 ( At least for a while).

Because one allele is producing p53 protein, that protein will detect the damage of chromosome break. Then p53 arrest the cell in G1 to repair the damage.