Final answer:
Crossing over is an exchange of genetic material between homologous chromosomes during prophase I of meiosis I, leading to increased genetic variation among offspring.
Step-by-step explanation:
Crossing Over in Meiosis
Crossing over is a crucial process that occurs during prophase I of meiosis I. It involves the exchange of genetic material between non-sister chromatids of homologous chromosomes. During prophase I, homologous chromosomes align gene-for-gene, forming a tetrad structure with four chromatids. It is at this point that sections of DNA can be broken off and reattached to corresponding positions on a homologous chromosome, a process also referred to as recombination. This exchange can occur multiple times, generating recombinant chromosomes that carry new combinations of alleles, thereby increasing the genetic variation among offspring.
Crossing over contributes to the pool of genetic diversity within a population, which is essential for evolution and adaptation. Furthermore, it is important for the normal segregation of chromosomes during the later stages of meiosis.