Order of meiotic divisions In meiosis, daughter cells arise through two successive divisions. Which statement correctly describes the order of these divisions?
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AFirst division is equational; second is reductional
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BFirst division is reductional; second is equational
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CBoth divisions are reductional
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DBoth divisions are equational
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ENeither division changes ploidy
Answer
Correct Answer: First division is reductional; second is equational
Explanation
Introduction / Context:Meiosis ensures halving of chromosome number for sexual reproduction. Knowing which division reduces ploidy and which separates sister chromatids is central to interpreting genetic outcomes and nondisjunction errors.
Given Data / Assumptions:
- Meiosis consists of meiosis I and meiosis II.
- Homologous chromosomes pair and recombine before segregation.
- Sister chromatids remain together through meiosis I (except at chiasmata).
Concept / Approach:Meiosis I is reductional: homologs segregate to different daughter cells, reducing 2n to n. Meiosis II is equational: sister chromatids separate, akin to mitosis, preserving haploid number.
Step-by-Step Solution:
Identify the stage that halves chromosome number: meiosis I (reductional).Identify the stage that separates sister chromatids: meiosis II (equational).Choose the option that states “first reductional, second equational.”Verification / Alternative check:Most textbooks refer to meiosis I as the reduction division and meiosis II as the equational division.
Why Other Options Are Wrong:
- Equational first then reductional is incorrect.
- Two reductional or two equational divisions do not describe standard meiosis.
- Nondisjunction exceptions exist but do not redefine the canonical scheme.
Common Pitfalls:Confusing chromatid and homolog separation due to both involving “pairs.”
Final Answer:First division is reductional; second is equational