Respuesta :
Crossing over occurs in the first stage of meiosis which would be Prophase I.
The correct answer is option D. Prophase I
The crossing over is a phenomena, which occur in the cells undergoing meiosis. In the process of crossing over, the exchange of the genetic material takes place between the sister chromatids. This process takes place in the prophase 1 stage of meiosis 1 in the gametes. The exchange of genetic material between chromatids cause recombination, and hence, genetic variation.
