Question

At the metaphase plate, during metaphase II of meiosis, there are:
A. Chromosomes consisting of one chromatid
B. Unpaired duplicated chromosomes
C. Bivalents (tetrads)
D. Homologous pairs of chromosomes

Answer 1

Hint: Similar to phase 1 of the meiotic cell division, in Meiosis I, Meiosis II (reduction cell division) also consists of 4 stages. Meiosis II relates to the mitotic cell division.

Complete Answer:
The chromosomes become arranged on the metaphase plate, similar to that in mitosis, and are attached to the fully formed spindle. The four stages of meiosis II are as follows:-
1. Prophase II – It begins as soon as the daughter cells are formed, after cytokinesis. The chromosomes begin to condense, along with the disappearance of the Golgi apparatus & ER complex, and the nuclear membrane’s dissolution.
2. Metaphase II – The chromosomes get aligned at the equator, to form the metaphase plate.
3. Anaphase II - Now, there is a simultaneous splitting of the centromere of each chromosome and the sister chromatids are pulled away towards the opposite poles. As they move towards the poles, the kinetochore is at the leading edge with the chromosomal arms trailing.
4. Telophase II – The chromosomes again dissolve into a lump and a nuclear envelope develops around it. This phase ends the complete process of meiosis, followed by cytokinesis; resulting in the formation of 4 haploid daughter cells.

Option A: Chromosomes consisting of one chromatid do not exist. Chromosomes carry two chromatids always. Therefore, this is the incorrect option.

Option B: The chromosomes get aligned at the equator, to form the metaphase plate. All cells in Meiosis II have their DNA contents reduced to half. In metaphase II also, the metaphase plate consists of only one copy of a duplicated homologous chromosome. Therefore, this is the correct option.

Option C: It is in Prophase I tetrads or bivalents are found and not in metaphase II, therefore, this is the incorrect option.

Option D: It is in Prophase II homologous chromosomes are found and not in metaphase II, therefore, this is the incorrect option.

Thus, the correct option is B) Unpaired duplicated chromosomes.

Note: In humans 23 pairs of chromosomes, the number of chromosomes remains unchanged from the beginning till the end of meiosis II. Meiosis does not allow the accumulation of chromosomes in the Zygotic nuclei, by reducing the number of chromosomes in the gametes to half of their parent germ cells.