Bacteria were grown in a medium containing heavy isotope of nitrogen (N15) for many generations and all their DNA contained heavy nitrogen only. A bacterium of this type was transferred to normal medium and allowed to duplicate. After two divisions of heavy DNA:
Correct answer: B. Two daughter cells have normal DNA and the other two have heavy DNA
- A. Only one daughter cell will have heavy DNA
- B. Two daughter cells have normal DNA and the other two have heavy DNA
- C. All daughter cells have heavy DNA
- D. All daughter cells contain hybrid DNA
Explanation
Duplication of DNA is by the semi-conservative method that was first shown in escherichia coli and later it was observed in higher organisms such as plants and animals.The DNA extracted from the first generation after the transfer from N15 medium to normal medium had a hybrid and or intermediate only and the DNA extracted from the second generation has equal amounts of hybrid DNA and normal DNA. So, the correct answer is ' half daughter cells have heavy DNA and the other half have normal DNA'.
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About Chromosomes
Chromosomes are DNA-protein structures that carry genes and become visible during cell division. Coverage includes chromatin, centromeres, sister chromatids, homologous chromosomes, chromosome number, and the distinction between diploid and haploid cells, with links to DNA replication, mitosis and meiosis.
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