Final answer:
Meiosis is a two-phase process that reduces the number of chromosomes from diploid to haploid by separating homologous chromosomes in meiosis I and sister chromatids in meiosis II, creating four unique haploid cells.
Step-by-step explanation:
Meiosis and Chromosome Number Reduction
Meiosis is a specialized form of cell division that reduces the chromosome number by half, creating four unique haploid cells from a single diploid cell. This process is critical in sexual reproduction to ensure that offspring have the same number of chromosomes as their parents. The reduction occurs in two main phases: meiosis I and meiosis II.
Meiosis I: Reduction Division
During meiosis I, homologous chromosomes pair up and exchange genetic material in a process called crossing-over. After lining up at the metaphase plate, these homologous chromosomes are then segregated to opposite poles of the cell during anaphase I, leading to the reduction in the number of chromosome sets from diploid to haploid. Each resulting cell at the end of meiosis I contains one chromosome from each homologous pair.
Meiosis II: Separation of Sister Chromatids
Meiosis II is conceptually similar to mitosis, where sister chromatids are separated. This second division does not further reduce the number of chromosomes; instead, it ensures each haploid cell has only one copy of each chromosome. The end result of meiosis II is four genetically distinct haploid cells that can develop into gametes.
During the entire process, from a diploid starting cell with homologous chromosomes to haploid gametes with single chromosomes, meiosis maintains genetic diversity through crossing-over and independent assortment while also conserving the species' chromosome number.