The total mass of all DNA molecules in the 46 chromosomes of one human somatic cell is about 6 · 10^–9 mg. Determine what the mass of all DNA molecules in the nucleus is equal to during spermatogenesis before meiosis, after meiosis I and meiosis II. Explain the results.
1) In interphase, the amount of DNA doubles during the replication process. The total mass is doubled: 6 · 10^−9 mg · 2 = 12 · 10^−9.
2) After meiosis I, the number of chromosomes in the cell becomes two times less, so the DNA mass is halved. And each chromosome consists of two chromatids.
The mass of DNA after meiosis I is 12 × 10^–9 mg: 2 = 6 × 10^–9.
After meiosis II, the chromosomes become monochromatic and the haploid set of chromosomes is contained in the nucleus of each sperm.
3) The total mass of DNA in the cell is 6 · 10^−9 mg: 2 = 3 · 10^−9.
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