What is Meiosis?
Meiosis is a specialized form of cell division that occurs in sexually reproducing organisms to produce gametes, such as sperm and eggs. Unlike mitosis, which creates identical diploid cells, meiosis reduces the chromosome number by half, resulting in haploid cells. This process ensures genetic continuity while introducing variation, playing a crucial role in evolution and biodiversity.
Stages of Meiosis
Meiosis consists of two sequential divisions: Meiosis I and Meiosis II. In Meiosis I (prophase, metaphase, anaphase, telophase), homologous chromosomes pair up, exchange genetic material through crossing over, and separate, halving the chromosome count. Meiosis II mirrors mitosis, where sister chromatids separate to form four unique haploid cells. This dual division is key to genetic recombination.
Practical Example: Meiosis in Humans
In human reproduction, meiosis occurs in the testes and ovaries. During sperm production, a diploid cell undergoes meiosis to yield four haploid sperm cells, each with 23 chromosomes. In egg formation, one diploid cell produces one viable egg and polar bodies. Crossing over during prophase I shuffles genes, so no two sperm or eggs are genetically identical, leading to diverse offspring combinations.
Role in Genetic Diversity
Meiosis drives genetic diversity through crossing over, which mixes alleles between homologous chromosomes, and independent assortment, where chromosomes segregate randomly. These mechanisms generate variation in gametes, ensuring offspring inherit unique gene combinations. This diversity enhances species adaptability, reduces inbreeding risks, and fuels natural selection, making meiosis foundational to evolutionary biology.