Answer:
D. Crossing over which alleles are exchanged
Step-by-step explanation:
Crossing over or recombination is the process by which segments of a chromosome (alleles) are exchanged between the non-sister chromatids of two homologous chromosomes. The process of crossing over solely occurs during meiotic division.
According to the image attached to this question, a pair of homologous chromosome (one black, one red) are shown. The alleles of two non-sister chromatids i.e. non-identical chromosomes are exchanged in such a way that one part of the first chromosome is present in the second and vice versa. This process is called CROSSING OVER.