Final answer:
The claim that mitotic crossing over is more frequent than meiotic crossing over is false; meiotic crossing over is a critical source of genetic diversity and typically occurs during meiosis I, whereas mitotic crossing over is rare.
Step-by-step explanation:
The statement that mitotic crossing over is more frequent than meiotic crossing over is false. Chromosomal crossover is a process that typically occurs during meiosis, specifically in prophase I of meiosis I, when homologous chromosomes pair up and exchange segments of their genetic material to form recombinant chromosomes. This exchange of genetic material between non-sister chromatids results in increased genetic variation. Crossover is facilitated by structures known as chiasmata and recombination nodules, which indicate the points where genetic material is exchanged. In contrast, although crossover can occur in mitosis, it is a rare event and does not contribute significantly to genetic diversity like meiotic crossover does.