Seedless Watermelons

I've always just assumed that the biologists just kept randomly making watermelons until they randomly found one without seeds, and from there they just used the same watermelon plant over and over again. Maybe that's how they do it, but it turns out what's happening is that the watermelon has three sets of chromosomes.

The same thing happens with mules and other hybridized species. Those with three sets of chromosomes are called triploids. They are always sterile since on third of the chromosomes cannot pair.

This has another interesting side-effect. Some hybridized species, like the whiptail lizard, develop parthenogenisis, a form of asexual reproduction through which the unfertilized female egg develops into an individual.

What's really fascinating about these lizard is that although they are all female, they tend to act out gender roles. The still perform courtship rituals, with those with low amounts of estrogen acting as males and those with high amounts of estrogen acting as females. Lizards that don't engaging in the courtship rituals tend to not reproduce.