During the zygotene stage of prophase-I of meiosis-I, homologous chromosomes synapse and are paired up. These paired homologous chromosomes are called bivalents. These paired homologous chromosomes align themselves at the equatorial plate of the cell during metaphase-I. Therefore, when observed through a microscope, cells are shown lined up two by two. During meiosis-II and mitosis, individual chromosomes with two sister chromatids are aligned at the cell's equator in metaphase.
