23. A special kind of cellular division, it occurs only in the sex cells (sex cells: sperm and eggs) and produces gametes.

Question

BlackTom AI · Accepted Answer

Meiosis produces haploid gametes through two successive divisions (meiosis I and II), halving the chromosome number and generating genetic variation by crossing over and independent assortment.

1) Relevant knowledge points and concepts
- Meiosis is a specialized form of cell division that occurs in the gonads (testes and ovaries) to make gametes (sperm and eggs).
- It consists of two rounds of division: meiosis I (reductional division: homologous chromosomes separate) and meiosis II (equational division: sister chromatids separate).
- Outcome: four genetically distinct haploid (n) daughter cells from one diploid (2n) parent cell.
- Key processes: homologous recombination (crossing over) and independent assortment, which increase genetic variation.

2) Step-by-step reasoning process
- The question specifies a division that "occurs only in the sex cells (sperm and eggs) and produces gametes." That defines a process that reduces chromosome number for sexual reproduction.
- Compare known cell-division types: mitosis produces two identical diploid somatic cells (not gametes); meiosis produces four haploid gametes; other listed words are not cell-division mechanisms.
- Therefore, the correct concept matching the description is meiosis.

3) Calculations/intermediate steps
- No numerical calculation is required. If tracking chromosome numbers: start 2n → after meiosis I = two cells each n (but with sister chromatids) → after meiosis II = four cells each n. This demonstrates the halving of chromosome number.

4) Why the correct answer is correct
- Meiosis is explicitly defined as the division that occurs in sex cells to produce gametes and reduces chromosome number from diploid to haploid, matching every element of the prompt.

5) Why other options are incorrect
- Prognosis: a medical term referring to predicted outcome, not a type of cell division.
- Mitosis: correct for somatic cell division, produces genetically identical diploid cells, not gametes.
- Gnosis: means knowledge or spiritual insight, unrelated to cell division.

6) Conclusion
- The correct answer is meiosis, which matches the provided answer.

23. A special kind of cellular division, it occurs only in the sex cells (sex cells: sperm and eggs) and produces gametes. 单项选择题

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