Final answer:
Crossing over is a meiosis-specific event that occurs during prophase I of meiosis I, where there is an exchange of genetic material between non-sister chromatids of homologous chromosomes; it doesn't occur in mitosis.
Step-by-step explanation:
The correct statement that is not true in relation to crossing over is 'It occurs during mitosis'. Crossing over is a meiosis-specific event and takes place during prophase I of meiosis I. This process involves the exchange of genetic material between non-sister chromatids of homologous chromosomes when they pair up to form a tetrad. The resulting recombinant chromosomes contribute to genetic variation in the haploid gametes produced after meiosis.
Crossing over does not occur during mitosis, which is the process that generates identical cells for growth and repair in multicellular organisms. The exchange of genetic material during crossing over contributes to the genetic diversity seen in sexual reproduction, as recombinant chromosomes contain different combinations of alleles than the original parental chromosomes.