Many plant cells have more than two complete sets of chromosomes in each cell. Explain how this might occur.

Polyploidy (more than two complete sets of chromosomes) is not rare among plants. For example, pollen grains may reach female flowers via animals or wind. In some cases, pollen grains from species with 4 complete sets of chromosomes will have 2 sets of chromosomes. Pollen grains may fuse with a female reproductive organ with 1 set of chromosome (so, female plant must have 2 sets of chromosomes). The resulting zygote will have 2 + 1 sets of chromosomes, so the plant will have 3 complete sets of chromosomes.