What happens in prophase 1 of meiosis?
Chromosomes begin to condense, and homologs loosely pair along their lengths, aligned gene by gene. The paired chromosomes are called tetrads which have 2 chromosomes and 4 chromatids. Crossing over (the exchange of corresponding segments of DNA molecules by non sister chromatids) is completed while homologs are in synapsis, held tightly together by proteins along their lengths. Synapsis ends in mid-prophase, and the chromosomes in each pair move apart slightly. Each homologous pair has one or more chiasmata, points where crossing over has occurred and the homologs are still associated due to cohesion between sister chromatids. Late in prophase 1, microtubules form from one pole or the other attach to the two kinetochore, protein structures at the centromeres of the two homologs. The homologous pairs then move toward the metaphase plate.