Summary
Highlights
Meiosis is a process where a diploid cell's chromosome number is halved, resulting in haploid cells called gametes (sperm and egg cells). The end result is four genetically unique haploid cells.
Before meiosis, the cell undergoes interphase, similar to mitosis. It starts with four DNA units (two maternal, two paternal) and six fictional genes. During the G1 stage, the cell grows. In the S stage, DNA replication occurs, doubling the DNA to eight units. The cell then continues to grow in the G2 stage.
Meiosis has two stages: Meiosis I and Meiosis II. In Prophase 1, the nucleus dissolves, and chromatin coils into chromosomes. A key event is synapsis, where homologous chromosomes pair up to form tetrads. This arrangement facilitates crossing over, the exchange of genetic material between non-sister chromatids, which generates genetic diversity crucial for species survival by preventing susceptibility to the same threats.
In Metaphase 1, the tetrads align along the cell's equator. Following this, in Anaphase 1, spindle fibers separate the homologous chromosomes, pulling entire chromosomes to opposite ends of the cell.
During Telophase 1, the nucleus may or may not reform. Cytokinesis then divides the single cell into two cells. Each new cell contains one of the two homologous chromosomes, and each now has four units of DNA (two chromosomes, each with two chromatids).
Meiosis II begins with Prophase 2, which is similar to mitosis. The nucleus, if reformed, dissolves again. In Metaphase 2, the remaining chromosomes align at the equator of each of the two cells.
Anaphase 2 sees the chromatids separating and being pulled to opposite ends of each cell, demonstrating Gregor Mendel's law of segregation. In Telophase 2, cytokinesis divides the two cells into four. The nucleus regrows in all four cells, and the chromatids uncoil into chromatin. Each of the final four haploid cells has two units of DNA and is genetically unique due to crossing over in Prophase 1.