Final answer:
Colchicine disrupts mitosis in diploid plants by binding to tubulin and preventing spindle formation, potentially leading to polyploidy and sympatric speciation through the creation of tetraploid offspring.
Step-by-step explanation:
When a diploid plant is treated with colchicine, it experiences disruption in mitosis, specifically during the metaphase stage where spindles are prevented from forming. Colchicine binds to tubulin protein, which is essential for spindle formation, thereby preventing the proper segregation of chromosomes during cell division. As colchicine inhibits mitosis, it can lead to polyploidy in plants, where the cells end up with more than two sets of chromosomes. This effect can result in autopolyploidy, which can cause sympatric speciation and the formation of tetraploid offspring that are reproductively isolated from the ancestral diploid species.