NEETBotanyCell Cycle and Cell Division
A diploid meiocyte in the G₁ phase of its cell cycle has 16 chromosomes and its DNA content is 20 pg. Which of the following correctly describes the configuration of this cell during the Pachytene stage of meiosis I?
Options
- A8 bivalents, 32 chromatids, 20 pg of DNA, and the appearance of recombination nodules
- B16 bivalents, 32 chromatids, 40 pg of DNA, and the formation of the synaptonemal complex
- C8 bivalents, 16 chromatids, 40 pg of DNA, and the formation of the synaptonemal complex
- D8 bivalents, 32 chromatids, 40 pg of DNA, and the appearance of recombination nodules
Correct answer
D. 8 bivalents, 32 chromatids, 40 pg of DNA, and the appearance of recombination nodules
Step-by-step solution
In the G₁ phase, the meiocyte has 2n = 16 chromosomes and a DNA content of 20 pg. During the S phase, DNA replication occurs, doubling the DNA content to 40 pg, but the chromosome number remains the same (16 chromosomes). Each chromosome now consists of two sister chromatids. During the Pachytene stage of Prophase I, the homologous chromosomes are paired. Since there are 16 chromosomes, they form 8 pairs, which are called bivalents (or tetrads). The total number of chromatids is 16 2 = 32 chromatids. The DNA conten