How many chromosomes are there in each human gamete cell at the end of Meiosis II?
The correct answer and explanation is :
At the end of Meiosis II, each human gamete cell contains 23 chromosomes.
Explanation:
Meiosis is the process that produces gametes (sperm and egg cells) for sexual reproduction. It involves two rounds of cell division: Meiosis I and Meiosis II. These divisions reduce the chromosome number by half, ensuring that when two gametes fuse during fertilization, the resulting zygote has the correct number of chromosomes (46 chromosomes).
- Meiosis I:
- This is the first division and is critical for reducing the chromosome number.
- Before meiosis begins, the parent cell has 46 chromosomes (23 pairs of homologous chromosomes).
- During Meiosis I, homologous chromosomes (one from each parent) are separated into different cells. The cell goes from being diploid (2n) to haploid (n).
- After Meiosis I, there are two daughter cells, each with 23 chromosomes, but each chromosome still consists of two sister chromatids.
- Meiosis II:
- This is similar to mitosis in that it involves the separation of sister chromatids, but it occurs in haploid cells.
- The two haploid cells produced in Meiosis I divide again during Meiosis II, but without any chromosome replication beforehand.
- In Meiosis II, the sister chromatids of each chromosome are separated, and the two haploid cells each divide to produce a total of four gametes.
- Each of the four resulting gametes has half the original number of chromosomes (23 chromosomes in humans). Importantly, each chromosome is now a single chromatid, as the sister chromatids have been separated.
Thus, by the end of Meiosis II, each human gamete has 23 chromosomes, which is the haploid number (n). When two gametes fuse during fertilization, the chromosome number is restored to the diploid number (46 chromosomes, or 23 pairs).