What is crossing over?

Crossing over refers to the specific process during meiosis where homologous chromosomes exchange segments of genetic material. This event occurs in prophase I, facilitating genetic variation in gametes, such as sperm and eggs. By exchanging segments, crossing over increases the diversity of alleles for the offspring, which is crucial for evolution and adaptation. This process is a vital mechanism for generating genetic diversity beyond what can be accomplished through the simple shuffling of chromosomes.

The other options, while related to cellular processes, do not accurately describe crossing over. For instance, mitosis is the process of cell division that results in two identical daughter cells, and the fusion of two cells refers to processes like fertilization or cell fusion, neither of which relates to the exchange of genetic material between chromosomes. Lastly, the division of a cell's cytoplasm, known as cytokinesis, occurs after mitosis or meiosis but does not involve the exchange of genes. Thus, the focus on homologous chromosomes exchanging segments in option C precisely captures the essence of crossing over in genetics.