The correct answer is option D, that is, crossing over.
Crossing over or chromosomal crossover refers to the exchange between the two homologous chromosomes sister chromatids, which results in recombinant chromosomes at the time of sexual reproduction.
It is one of the ultimate stages of genetic recombination that takes place in the pachytene stage of prophase I of meiosis at the time of a procedure known as synapsis.
