Crossing over happens specifically during the pachytene substage of prophase I. That's when homologous chromosomes are fully synapsed and the recombination nodules are active.
Honestly, I drill this into my students here in Kota until they can recite it in their sleep. But I always remember my own confusion back in school in Sikkim, staring at a diagram in the old biology book, the sunlight from the window making the page glow—I kept thinking it was during zygotene. It's a small, solid fact that holds firm, unlike my ancient projector that always chooses to fail during that very lesson.
#exams#study
Jump in to reply — no account needed.