Meiosis II is a specialized form of cell division, representing the second phase of a two-part cellular process. It ultimately leads to the generation of gametes, such as sperm and egg cells. This intricate division ensures the proper distribution of genetic material for sexual reproduction.
The Goal of Meiosis II
Meiosis I concludes with two haploid cells, each containing chromosomes that still consist of two sister chromatids. The primary objective of Meiosis II is to separate these sister chromatids, a process that closely resembles mitosis. This separation produces truly haploid cells, meaning each resulting cell contains only one set of chromosomes, and each chromosome has only one chromatid. This precise division is fundamental for maintaining the correct chromosome number across generations following fertilization and contributes to genetic diversity.
Prophase II
In Prophase II, chromosomes, still composed of two sister chromatids, begin to condense and become more compact. The nuclear envelope starts to break down. Concurrently, new spindle fibers, essential for chromosome movement, begin to form within the cell. This phase prepares the cell for the precise alignment and separation of its genetic contents.
Metaphase II
In Metaphase II, each chromosome, still made up of two sister chromatids, aligns individually along the central plane of the cell, known as the metaphase plate. Kinetochores, located at the centromere of each sister chromatid, attach to spindle fibers extending from opposite poles of the cell. This arrangement ensures that each sister chromatid will be pulled to opposing ends of the cell, leading to accurate chromosome segregation.
Anaphase II
In Anaphase II, the centromeres holding the sister chromatids together divide. Once separated, these formerly linked sister chromatids are now considered individual chromosomes. Spindle fibers, attached to the kinetochores of these newly independent chromosomes, shorten and pull them toward opposite poles of the cell. This movement effectively distributes a complete set of single-chromatid chromosomes to each forming pole.
Telophase II and Cytokinesis
In Telophase II, separated chromosomes arrive at opposite poles of the cell. Upon reaching the poles, chromosomes begin to decondense, unwinding and becoming less compact. New nuclear envelopes form around each set of chromosomes, creating distinct nuclei.
Following nuclear division, cytokinesis (the division of the cytoplasm) takes place. In animal cells, this involves the formation of a cleavage furrow that pinches the cell membrane inward, dividing the cell into two. This process results in four genetically unique haploid cells from the two cells that entered meiosis II. These four haploid cells are the final products of meiosis, functioning as gametes in sexual reproduction.