Question Detail
Question
The DNA content of a non-dividing diploid cell in the G1 phase of the cell cycle is measured. At metaphase II of meiosis, the DNA content of the same cell would be: a. half that of the G1 cell b. thrice that of the G1 cell c. the same as in the G1 cell d. twice that of the G1 cell
Correct Answer
Option A is the correct answer.
Detailed Explanation
A G1 diploid cell has a 2n amount of DNA. A cell at metaphase II is haploid and has undergone DNA replication, so its DNA content is 2n? Let's think: A G1 cell (2n) -> after S phase (4n) -> Meiosis I produces two cells, each with 2n DNA (still two chromatids per chromosome) -> Meiosis II separates chromatids. At metaphase II, the cell is haploid but each chromosome still has two chromatids, so the DNA content is 2c (where c is haploid content). The G1 cell had 2c (diploid, 2n). The metaphase II cell has 1c? I need to be careful. If G1 DNA = 2C (where C is haploid genome content). After S phase, it's 4C. After Meiosis I, each cell has 2C (still duplicated chromosomes). At metaphase II, the cell still has 2C DNA. So it's the SAME as the G1 cell? That can't be right because G1 is 2C diploid, metaphase II is 1C? No, metaphase II cell is haploid but chromosomes are still duplicated (sister chromatids). So it has 2 chromatids per chromosome, so DNA content is 2 * (1n DNA) = 2n worth of DNA. A G1 cell is 2n (diploid). So they are equal in DNA amount? Actually, DNA amount is measured by mass. A diploid G1 cell has 2x the DNA of a haploid gamete. A metaphase II cell has 2x the DNA of a haploid gamete because its chromosomes are duplicated. So a metaphase II cell has the same DNA content as a diploid G1 cell. So the answer should be c. the same as in the G1 cell.
Hint
Both have duplicated chromosomes? G1 does not have duplicated chromosomes. G1 is before S phase, so chromosomes are unduplicated. So G1 has 2C (diploid, 2n). Metaphase II: haploid (n) but each chromosome has 2 chromatids, so DNA content is 2 * (n) = 2C. So they are the same. Yes, answer is C.