Question

Which of the following statement is incorrect? (a) Prophase II is simpler than prophase I. (b) Prophase I is longer and complex than prophase of mitosis. (c) Nuclear membrane reappears in telophase I. (d) Anaphase II is not characterized by the splitting of centromere.

Short answer

The incorrect statement is (d): Anaphase II is not characterized by the splitting of centromere. In fact, Anaphase II is characterized by the splitting of the centromere.

Step-by-step solution

Understanding Prophase I and Prophase II

In meiosis, Prophase I is the first stage and is indeed longer and more complex than Prophase II. During Prophase I, chromosomes condense, homologous chromosomes pair up and exchange segments (crossing-over), and the nuclear envelope breaks down. Whereas, during Prophase II, which is part of the second meiotic division, no DNA replication occurs and it is simpler than Prophase I. Hence, Statements (a) and (b) are correct.

Understanding Telophase I

During Telophase I, the cells are divided into two, each containing a haploid set of chromosomes. In many organisms, the nuclear membrane reappears as the cell divides into two. Therefore, statement (c) is correct.

Understanding Anaphase II

During Anaphase II, the sister chromatids of each chromosome, which are still joined at the centromere, are pulled apart by the spindle apparatus and move to the opposite poles of the cell. This indicates that the splitting of the centromere indeed characterizes Anaphase II. Therefore, statement (d) is incorrect as it suggests that the centromere does not split during Anaphase II

Key concepts

Prophase I

In the process of meiosis, Prophase I is a critical and complex stage where several key activities take place to ensure genetic variation in the resulting gametes. Unlike Prophase of mitosis, Prophase I is both longer and more involved, due to its unique processes. Here, chromosomes condense and become visible under a microscope, marking the start of prophase. An essential feature of Prophase I is the pairing of homologous chromosomes in a process called synapsis, which facilitates the exchange of genetic material through crossing-over. This exchange occurs at structures called chiasmata and results in the recombination of genetic material, contributing to genetic diversity. Additionally, the nuclear envelope breaks down, allowing the spindle fibers to attach to the chromosomes. The complexity and duration of Prophase I distinguish it from Prophase II, which is significantly simpler and does not involve DNA replication.

Anaphase II

Anaphase II occurs during the second meiotic division and is characterized by several important changes in the cell. In this stage, the sister chromatids, which have remained together since Prophase I, are finally separated. This separation is due to the splitting of centromeres, allowing the spindle fibers to pull the chromatids toward opposite poles of the cell. The movement of chromatids to opposite ends ensures that each new cell will receive an equal and identical set of chromosomes. This step, therefore, doubles the number of cells and is pivotal for producing gametes with the proper chromosome number. Statements that suggest the centromere does not split in Anaphase II are incorrect, as the splitting and separation of the chromatids define this crucial stage.

Telophase I

In Telophase I, the first meiotic division nears completion, resulting in the formation of two separate cells. Each of these cells contains a haploid number of chromosomes, meaning that they have one chromosome from each homologous pair. As the chromosomes reach opposite poles, they begin to de-condense and become less visible under the microscope. In many organisms, the nuclear membrane reforms around each set of chromosomes, which is a key feature distinguishing Telophase I from other phases of meiosis. This reformation of the nuclear membrane signals the near end of the first meiotic division and prepares the cells for the subsequent phases leading into the second division.

• The reappearance of the nuclear membrane provides structural boundaries for the newly formed nuclei within the daughter cells.
• Although the cells are still connected by a cytoplasmic bridge, cytokinesis may begin to fully separate the two cells.

Thus, Telophase I is crucial for transitioning from the reduction division to the preparation for division two.