Question

A group of cells is assayed for DNA content and is found to have an average of 8 picograms of DNA per nucleus. Picograms are a relatively small unit of weight. You stimulate your cells to enter mitosis, and keep checking for DNA content. 1 point each

How many picograms per nucleus would be found at the end of G1? _____________

How many picograms per nucleus would be found at the end of S? _____________

How many picograms per nucleus would be found at the end of G2? _____________

How many picograms per nucleus would be found at the end of mitosis? _____________

Answer 1

Ans. #1. The cell has not duplicated its DNA by the end of G1 phase. So, DNA content at the end of G1 phase remains the same as initial DNA content.

So,

            DNA content per nucleus at the end of G1 = 8 pg

#2. The cell duplicates its DNA in S. So, DNA content at the end of S phase is double to that of initial DNA content.

So,

            DNA content per nucleus at the end of S = 2 x 8 pg = 16 pg

#3. DNA is duplicated only is S-phase and no other phases. The cell neither duplicates it DNA nor divide in G2 phase. So, DNA content at the end of G2 phase is the same as that of S phase.

So,

            DNA content per nucleus at the end of G2 = 16 pg

#4. DNA is duplicated only is S-phase and no other phases. The cell does not duplicate it DNA in M-phase but divides its nucleus into two daughter nuclei by the end of mitosis. So, DNA content at the end of mitosis phase is half- of that of G2 phase.

So,

            DNA content per nucleus at the end of Mitosis = ½ x 16 pg = 8 pg