Questions & Answers

What will be the amount of DNA in a pollen grain if its mother cell has 32 picogram DNA in G2 phase?
A) 16 pg
B) 32 pg
C) 8 pg
D) 4 pg

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Hint: Deoxyribonucleic acid (DNA) is a molecule made up of two polynucleotide chains that curl together to create a double helix which contains genetic code for the formation, operation, development, and replication of all kinds of organisms and viruses. Nucleic acids include DNA and ribonucleic acid (RNA).

Complete answer:
The G2 phase is also referred to as Gap 2 phase or Growth 2 phase, is the third interphase sub-phase in the cell cycle that occurs just before mitosis.

The G2 phase follows the S phase. DNA synthesis occurs during the S phase. The quantity of DNA doubles, while the cell's chromosomal number or diploid content stays same. So, if the mother cell has 32 picograms (pg) of DNA in G 2 that indicates the cell initially had 16 picograms of DNA.

The mother cell that produces the pollen grain is diploid, and meiosis occurs to make haploid pollen grains. So, if the diploid mother cell has 16 picograms of DNA, the quantity of DNA in haploid pollen grain is half of that, or 8 picograms.

Therefore, the correct answer is 8 pg which is option ‘C’.

Note: The G2 occurs after the complete conclusion of S phase, during which the DNA of the cell is reproduced. G2 phase concludes with the commencement of prophase, the first phase of mitosis in which chromatin condenses into chromosomes. The G2 phase is characterised by fast cell growth and protein synthesis as the cell prepares for mitosis. Surprisingly, the G2 phase is not required for all cell types, since some (especially immature Xenopus embryos and certain malignancies) progress directly from DNA replication to mitosis.