Final answer:
Crossing over is the process that explains exceptions to the principle of independent assortment.
Step-by-step explanation:
Exceptions to the principle of independent assortment were discovered and explained by crossing over. Crossing over is the exchange of genetic material between homologous chromosomes during meiosis. It results in the recombination of alleles and the creation of new gene combinations, which leads to deviations from Mendel's principle of independent assortment.