36.3
Meiosis II
Meiosis II is the second cell division of meiosis, which can either start immediately after meiosis I, without any prior DNA synthesis, or, after a brief time interval called interkinesis.
Like mitosis, meiosis II follows an equational division, except in meiosis II, a haploid cell gets divided into two haploid cells.
Meiosis II is divided into four stages – prophase II, metaphase II, anaphase II, and telophase II.
Prophase II is characterized by the thickening and shortening of the chromosomes. Centrioles move to opposite poles and begin to form a meiotic spindle which is followed by the dissolution of the nuclear membrane.
In metaphase II, the chromosomes line up at the equatorial plane of the cell. Unlike in mitosis, the sister chromatids constituting each chromosome are non-identical as they underwent recombination in meiosis I.
In anaphase II, the cohesin complex that holds the two sister chromatids together, breaks down, allowing single chromatids to move towards opposite poles.
Like homologous chromosomes in meiosis I, these sister chromatids also undergo independent assortment and contribute to the production of the genetically unique gametes.
Telophase II is marked by the reformation of the nuclear envelope and decondensation of the chromatids.
Finally, cytokinesis divides each parental cell into two haploid cells. These haploid cells can act as gametes in sexual reproduction in animals or as spores in plants, with their unique genetic makeup helping to increase the genetic diversity.
Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for meiosis II are similar to mitosis, except that meiosis II occurs in haploid cells, whereas mitosis occurs in diploid cells.
The timing and cell division patterns of meiosis differ between males and females. In male meiosis, the centrosomes are part of the formation of the meiotic spindle. However, in oocytes, including that of humans, Drosophila, and mice, the meiotic spindle forms without centrosomes. Further, in mammalian oocytes, cyclin A2 plays a vital role in the stabilization of the meiotic spindle and the separation of the sister chromatids in anaphase II. In mouse oocytes, inhibition of cyclin A2 results in disordered spindle formation and failure of segregation of sister chromatids.
Telophase II is followed by cytokinesis, which completes one meiosis cycle with the production of four haploid daughter cells. In male meiosis, all four daughter cells have equal amounts of cytoplasm; however, in female gametes, asymmetric distribution of the cytoplasm occurs in meiosis I, which leads to the production of an egg cell and a haploid polar body. The egg cell undergoes meiosis II only after fertilization and produces the haploid mature ovum and the secondary polar body. The mature ovum then fuses with the sperm and forms the diploid zygote.
Meiosis II is the second cell division of meiosis, which can either start immediately after meiosis I, without any prior DNA synthesis, or, after a brief time interval called interkinesis.
Like mitosis, meiosis II follows an equational division, except in meiosis II, a haploid cell gets divided into two haploid cells.
Meiosis II is divided into four stages – prophase II, metaphase II, anaphase II, and telophase II.
Prophase II is characterized by the thickening and shortening of the chromosomes. Centrioles move to opposite poles and begin to form a meiotic spindle which is followed by the dissolution of the nuclear membrane.
In metaphase II, the chromosomes line up at the equatorial plane of the cell. Unlike in mitosis, the sister chromatids constituting each chromosome are non-identical as they underwent recombination in meiosis I.
In anaphase II, the cohesin complex that holds the two sister chromatids together, breaks down, allowing single chromatids to move towards opposite poles.
Like homologous chromosomes in meiosis I, these sister chromatids also undergo independent assortment and contribute to the production of the genetically unique gametes.
Telophase II is marked by the reformation of the nuclear envelope and decondensation of the chromatids.
Finally, cytokinesis divides each parental cell into two haploid cells. These haploid cells can act as gametes in sexual reproduction in animals or as spores in plants, with their unique genetic makeup helping to increase the genetic diversity.
- Meiosis II - Second phase of meiosis involving cell division and creation of haploid gametes.
- Haploid Gametes - Unique reproductive cells produced by meiosis II.
- Sister Chromatids - Identical strands of DNA separated during meiosis II.
- Cytokinesis Meiosis II - Final step in cell division that follows telophase II.
- Female Meiosis - Meiosis process in females, leading to the production of egg cells.
- Define Meiosis II – Explain the process and outcome of this cellular phase (e.g., meiosis ii).
- Contrast Meiosis II vs Mitosis – Explain the differences in these two cell division processes (e.g.,meiosis ii vs mitosis).
- Explore the Stages – Describe details of each stage (e.g., anaphase ii, telophase ii).
- Explain Gametes – Elaboration on the formation and role of haploid gametes.
- Apply in Context – Describe the application within the context of cell biology and reproduction.
- What is Meiosis II and how does it result in the formation of haploid gametes?
- What are the key differences between meiosis II and mitosis?
- What roles do the sister chromatids and cytokinesis play in meiosis II?
From Chapter 36:
