Meiosis II

During prophase II, chromosomes thicken and shorten as centrioles move to opposite poles to form the meiotic spindle. The nuclear membrane dissolves, preparing the cell for chromosome alignment. These events mirror mitosis but occur in haploid cells rather than diploid cells.

The cohesin protein complex holding sister chromatids together breaks down during anaphase II, allowing individual chromatids to move toward opposite poles. These chromatids undergo independent assortment, contributing to genetically unique gamete production and increasing genetic diversity in offspring throughout sexual reproduction.

Sister chromatids are non-identical because they underwent recombination during meiosis I, exchanging genetic material between homologous chromosomes. This genetic exchange, known as crossing over, ensures that each chromatid carries a unique combination of alleles before they separate in meiosis II.

In male meiosis, all four daughter cells receive equal cytoplasm, while female meiosis produces asymmetric cytokinesis, creating one egg cell and a polar body. Additionally, in female oocytes, the meiotic spindle forms without centrosomes, and cyclin A2 stabilizes spindle formation and sister chromatid separation.

Meiosis II can begin immediately after meiosis I without DNA synthesis, or after a brief interval called interkinesis. This timing variation allows the cell to prepare for the second division while maintaining the haploid chromosome number established during meiosis I.

Meiosis II produces four genetically unique haploid cells through cytokinesis. In animals, these cells function as gametes; in plants, they become spores. Their unique genetic makeup, resulting from recombination and independent assortment, increases genetic diversity in sexual reproduction and organism variation.

During telophase II, the nuclear envelope reforms and chromatids decondense back into chromatin. Cytokinesis then divides each cell into two haploid daughter cells, completing meiosis with four total haploid gametes ready for sexual reproduction, spore formation, and genetic contribution to offspring.