Question

Meiosis I is reductional division. Meiosis II is equational division due to

• A. pairing of homologous chromosomes
• B. crossing over
• C. separation of chromatids
• D. disjunction of homologous chromosomes.

Answer 1

The Correct Option is C

To understand why Meiosis I is called reductional division and Meiosis II is known as equational division, we need to explore the stages of meiosis and the changes that occur during each phase.

Meiosis Overview: 

Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of gametes or spores. It consists of two sequential stages: Meiosis I and Meiosis II.

1. Meiosis I - Reductional Division: This phase reduces the chromosome number by half. It includes several stages: Prophase I, Metaphase I, Anaphase I, and Telophase I.
   • During Anaphase I, homologous chromosomes (each consisting of two sister chromatids) are separated and distributed to two different daughter cells. Thus, the chromosome number is reduced from diploid (2n) to haploid (n).
2. Meiosis II - Equational Division: This division is similar to mitosis. It includes the stages: Prophase II, Metaphase II, Anaphase II, and Telophase II.
   • During Anaphase II, the sister chromatids of each chromosome are separated and move toward opposite poles. Since the chromosome number remains unchanged in this division (sister chromatids separate), it is termed as equational division.

Explanation of Answer:

The question asks why Meiosis II is called equational division. The correct answer is the "separation of chromatids." In Meiosis II, the separation of sister chromatids occurs, akin to what happens in mitosis. As a result, the number of chromosomes stays the same between the mother cell and the daughter cells post-Meiosis II, which is why it's referred to as equational. This contrasts with Meiosis I, where the homologous chromosomes are separated and the chromosome number is halved, making it reductional.

Elimination of Other Options:

• Pairing of homologous chromosomes: Occurs in Prophase I of Meiosis I, not in Meiosis II.
• Crossing over: Also occurs during Prophase I of Meiosis I, crucial for genetic recombination.
• Disjunction of homologous chromosomes: This refers to the separation of homologous chromosomes during Anaphase I of Meiosis I.

Hence, the correct answer is the "separation of chromatids" in Meiosis II.