P is stage of meiosis in which the crossing over takes place and Q is the stage in which the terminal chiasmata are at the equator. P and Q are respectively

In a meiotic division, crossing over occurs in Pachytene  by the action of recombinase. The number of chiasmata decrease in diakinesis due to terminalization and terminal chiasma remains at the telomeres of non-sister chromatids. Chiasmata are arranged at equator in Metaphase I.