This has led to the deliberate creation of polyploid varieties of such plants as watermelons, marigolds, and snapdragons. Polyploidy can be induced by treating dividing cells with colchicine. This drug disrupts microtubules and thus prevents the formation of a spindle. Consequently, the duplicated chromosomes fail to separate in mitosis. Onion cells exposed to colchicine for several days may have over 1000 chromosomes inside.
Polyploidy is much rarer in animals.
It is found in some insects, amphibians, and reptiles. Until recently, no polyploid mammal was known. The liver cells of the Argentinian rat are larger than those of its diploid relatives, and its sperm are huge in comparison.