Final answer:
Crossover during meiosis leads to an exchange of genetic material and the creation of new combinations of genes. After one crossing over event, four types of chromatids are produced.
Step-by-step explanation:
Crossover during meiosis leads to an exchange of genetic material between non-sister chromatids of homologous chromosomes. This process, known as recombination, creates new combinations of genes and increases genetic variation. When one crossover occurs, two recombinant chromatids and two non-recombinant chromatids are produced. So, after one crossing over event, four types of chromatids are produced.