You have studied mitosis in onion root tip cells. It has 16 chromosomes in each cell. Can you tell how many chromosomes will the cell have at G1 phase, after S phase and after M phase? Also what will be the DNA content of the cells at G1, after S and at G2, if the content after M phase is 2C?

Dear Student,

At G1 phase, there will be 16 chromosomes as no DNA replication has taken place. After S Phase, the DNA content doubles but chromosome number still remains same here 14. After completion of M phase, the number of chromosomes will be 32 with each daughter cell having the same number of chromosomes as that of parent i.e 16.

1  phase is the interval phase between mitosis and initiation of DNA replication. The initial amount of DNA is denoted as 2C ( C, is the haploid DNA content) which is then increases to 4C at the completion of S-phase. However there is no increase in the chromosome number; if the cell had a diploid or 2n number of chromosomes at G 1 , even after S-phase the number of chromosomes remains the same that is 2n. So if content after M-phase is 2C it will remain as 2C only.   

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