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Solution


Q.

A somatic cell that has just completed the S phase of its cell cycle, as compared to a gamete of the same species, has  [2015]
1 twice the number of chromosomes and four times the amount of DNA  
2 four times the number of chromosomes and twice the amount of DNA  
3 twice the number of chromosomes and twice the amount of DNA  
4 same number of chromosomes but twice the amount of DNA  

Ans.

(1)

In diploid cells (somatic cells) during G1 phase, DNA content is 2C and chromosome number is 2n whereas in haploid cells (gamete) during G1 phase, DNA content is 1C and chromosome number is n. S phase is marked by replication of DNA and the amount of DNA per cell is doubled, i.e., it becomes 4C in somatic cells, whereas chromosome number remains same, i.e., 2n. Thus, a somatic cell which has just completed S phase, will have 4C DNA content but 2n chromosome number, while the gamete cell has 1C DNA content and n chromosome number.