Crossing over occurs between:

a. sister chromatids is the same chromosome

b. two different kinds of tetrads

c. two different kinds of chromosomes

d. non sister chromatids of a tetrad

e. two daughter nuclei

crossing over, process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosis. At that stage each chromosome has replicated into two strands called sister chromatids.