Question

Analyse the events during every stage of cell cycle and notice how the following two parameters change
(i) Number of chromosomes (N) per cell
(ii) Amount of DNA content (C) per cell

Answer 1

Meiosis:

1. Meiosis is called reductional division because the chromosome number of halved. ​
2. During meiosis, the number of chromosomes and the amount of DNA in a cell changes in the two phases of meiosis.

Part (i): Number of chromosomes (N) per cell:

1. The number of chromosome in a diploid cell can be considered as 2N.
   
2. During anaphase I of the meiotic cycle, the homologous chromosomes separate and start moving toward their respective poles.
   
3. This is why the chromosome number gets halved here and the number of chromosome becomes N.
   
4. The same number of chromosome is maintained after the meiosis II phase because the chromosome only breaks with two sister chromatids moving to the two poles.
   
5. Therefore number of chromosome produced per cell at the end of meiosis II is N.
   

Part (ii): Amount of DNA content (C) per cell:

1. Let the DNA content of the cell at the start of meiosis be 2C.
   
2. During the S phase, synthesis of DNA occurs which makes the DNA content become 4C.
   
3. At the end of meiosis I, the DNA content in the cell again becomes halved, which is 2C.
   
4. After meiosis II, the DNA content again gets halved and hence final cells produced after meiosis have DNA content as C.