Which event takes place in meiotic metaphase I, but not in mitotic metaphase?
A Homologous chromosomes align at the cell equator.
B Homologous chromosomes undergo crossing-over.
C Meiotic metaphase I and mitotic metaphase have no differences.
D Sister chromatids align at the cell equator. none of the above
The correct answer and explanation is:
The correct answer is A. Homologous chromosomes align at the cell equator.
Explanation:
In meiosis and mitosis, metaphase is a stage in which chromosomes align at the cell equator. However, the alignment process in meiosis I differs from that in mitosis. During mitotic metaphase, chromosomes consisting of two sister chromatids align at the equator of the cell, with each chromosome lined up independently. The key difference lies in meiotic metaphase I, where homologous chromosomes (chromosomes that are similar in shape, size, and genetic content, one inherited from each parent) align together at the cell’s equator. This process is known as synapsis, and the homologous chromosomes are positioned next to each other in pairs. This alignment of homologous chromosomes is not seen in mitotic metaphase.
- In mitosis, the process involves only sister chromatids of the same chromosome, each with identical genetic material. These chromatids align independently at the cell’s center and later separate into two daughter cells.
- In meiosis I, homologous chromosomes are arranged in pairs, and each homologous chromosome aligns at the metaphase plate. After this alignment, they undergo independent assortment, a critical process where different combinations of maternal and paternal chromosomes are sorted into the daughter cells, leading to genetic diversity. This alignment and pairing of homologous chromosomes do not occur in mitosis.
The other options listed do not accurately describe differences between meiotic metaphase I and mitotic metaphase:
- B is incorrect because crossing-over happens during prophase I of meiosis, not during metaphase I.
- C is incorrect because meiosis and mitosis are distinct processes, and they have key differences in chromosome behavior.
- D is incorrect because sister chromatids align in both meiosis II and mitosis, but not in meiosis I, where homologous chromosomes align instead.
In conclusion, the main distinction in metaphase I of meiosis is the alignment of homologous chromosomes, which does not occur in mitotic metaphase.