Final answer:
During metaphase of mitosis, sister chromatids align at the equator, while during metaphase I of meiosis I, homologous chromosomes line up side-by-side. The correct answer is B) Homologous chromosomes.
Step-by-step explanation:
During metaphase of mitosis, sister chromatids line up single file at the cell's equator. Conversely, during metaphase I of meiosis I, homologous chromosomes line up side-by-side. Hence, the correct answer to the question is B) Homologous chromosomes.
Metaphase I is distinct in that spindle fibers attach to the paired homologous chromosomes, and these chromosomes align along the cell's equator. This is a critical step as it ensures the subsequent separation of these chromosome pairs during anaphase I. In contrast, during metaphase of both mitosis and meiosis II, individual sister chromatids, not pairs, align at the equator for their eventual separation.