Final answer:
During meiosis I, homologous chromosomes line up as tetrads on the metaphase plate, with spindle fibers attaching to each homolog's kinetochores from opposite poles. This contrasts with mitosis and meiosis II, where sister chromatids align along the metaphase plate with kinetochore fibers attached to their kinetochores.
Step-by-step explanation:
The way metaphase chromosomes line up during meiosis differs significantly from their alignment during mitosis. In meiosis I, homologous chromosomes pair up and are held together by a synaptonemal complex during a process called synapsis. This pairing results in structures known as tetrads, where two homologous chromosomes, each consisting of a pair of sister chromatids, come together.
During metaphase I of meiosis, these tetrads align at the metaphase plate in such a way that kinetochore fibers from opposite spindle poles attach to each homolog's kinetochores. This formation ensures that homologous chromosomes, rather than sister chromatids, are separated during the subsequent anaphase I, leading to a reduction in chromosome number by half. In contrast, during metaphase of mitosis and meiosis II, it is the sister chromatids that align along the metaphase plate, with kinetochore fibers attaching to kinetochores of sister chromatids, not homologous chromosomes.
The presence of crossover between nonsister chromatids and the lining up of tetrads introduces genetic variation in meiosis, which does not occur in mitosis. Moreover, meiosis I is a reduction division, halving the number of chromosomes, unlike mitosis which maintains the diploid number.