Metaphase II

Definition

Metaphase II is a stage of meiosis where chromosomes align at the equatorial plane of the cell, ensuring proper segregation during the second meiotic division. This phase occurs after telophase I and before anaphase II, and is critical for maintaining genetic diversity in gametes by ensuring that sister chromatids are correctly positioned for separation.

5 Must Know Facts For Your Next Test

1. During metaphase II, chromosomes are maximally condensed and aligned along the cell's equatorial plane, making them visible under a microscope.
2. Each chromosome at this stage consists of two sister chromatids, which are held together at the centromere until they are separated during anaphase II.
3. The alignment during metaphase II is essential for ensuring that each daughter cell receives an equal and accurate distribution of chromosomes.
4. Metaphase II is similar to metaphase in mitosis, but it involves haploid cells, each with half the original chromosome number.
5. Errors in chromosome alignment during metaphase II can lead to aneuploidy, resulting in gametes with abnormal numbers of chromosomes.

Review Questions

• How does the process of chromosome alignment in metaphase II differ from that in mitosis?
  • In metaphase II, chromosomes align at the cell's equatorial plane similarly to mitosis; however, the key difference lies in the chromosome number. In metaphase II, each chromosome consists of two sister chromatids and is part of a haploid cell, while in mitosis, cells are diploid with a full set of chromosomes. This distinction impacts genetic diversity since meiosis produces genetically unique gametes compared to the identical daughter cells produced by mitosis.
• What role do kinetochores play during metaphase II and why are they important for successful cell division?
  • Kinetochores are crucial during metaphase II as they serve as attachment points for spindle fibers that pull chromosomes apart. Each chromatid has its own kinetochore that connects to spindle fibers emanating from opposite poles of the cell. This attachment ensures that when anaphase II begins, sister chromatids are pulled apart correctly, maintaining the integrity of genetic material in the resulting gametes. If kinetochores do not function properly, it can lead to unequal segregation of chromosomes.
• Evaluate the implications of improper chromosome alignment during metaphase II on genetic diversity and potential disorders.
  • Improper chromosome alignment during metaphase II can have significant implications for genetic diversity and health. If chromosomes do not align correctly, it can result in aneuploidy, where gametes have too many or too few chromosomes. This condition can lead to disorders such as Down syndrome or Turner syndrome when such gametes participate in fertilization. Additionally, errors can reduce genetic variation in offspring, which is vital for evolution and adaptation. Therefore, precise alignment during this stage is critical for both individual health and species diversity.

Related terms

Meiosis: A specialized type of cell division that reduces the chromosome number by half, creating four genetically diverse gametes.

Chromatid: Each of the two identical halves of a replicated chromosome, which are separated during meiosis II.

Kinetochore:

A protein structure on the chromosome where the spindle fibers attach during cell division, crucial for chromosome movement.