Meiosis: The Process of Creating Sex Cells
Meiosis begins with Prophase I, where chromosomes condense and form tetrads (pairs of homologous chromosomes). This is when crossing over occurs—genetic material is exchanged between chromosomes, creating new genetic combinations. This natural process increases genetic diversity and isn't considered a mutation.
In Metaphase I, the nuclear membrane disappears while centrioles move to opposite poles. Tetrads line up along the cell's equator as spindle fibers attach to chromosomes. During Anaphase I, homologous chromosomes separate and are pulled to opposite sides of the cell.
Telophase I and Cytokinesis complete the first division. Chromosomes reach the poles, spindle fibers dissolve, and the nucleus reforms. The cytoplasm divides, producing two haploid cells (cells with half the chromosome number).
💡 The key difference between mitosis and meiosis appears in Anaphase I, when homologous chromosomes separate instead of sister chromatids. This is how the chromosome number is reduced!
The second division (Prophase II through Telophase II) resembles mitosis. The nucleus dissolves again, chromosomes line up at the equator, and sister chromatids finally separate. By the end, four haploid cells are produced, each containing one set of chromosomes.