AP BIOLOGY

Detailed explanation-1: -Crossing over occurs during pachytene stage between non sister chromatids of a pair of homologous chromosomes. Diplotene is characterised by appearance of chiasma marking the locations at which crossing over has already occurred in the pachytene stage.

Detailed explanation-2: -Crossing over is an enzyme-mediated process, where the exchange of genetic material between non-sister chromatids of homologous chromosomes takes place. It occurs at the pachytene stage of prophase I of meiosis.

Detailed explanation-3: -Crossing over occurs during the pachytene stage of prophase in meiosis, however the chiasma are visible during. No worries!