Warren Booth | Live Science
A female boa in a pet store in Tennessee has just given birth to her second litter of offspring in as many years. She began giving birth when male boas were introduced into her environment. Most would assume that the female got up to something when the shopkeeper's back was turned, but the boa's offspring were unusual. For one thing, they were all female. For another, they all had the same coloring as their mother, even though caramel coloration is a recessive trait among boa constrictors.io9 via LiveScience
Scientists were intrigued enough to investigate, and confirmed that the female boa had reproduced through parthenogenesis (self-fertilization). The eggs of female boas only have half a full set of chromosomes, but it appeared that two eggs had fused and formed a full complement of genes.
What's more, the baby snakes had a combination of genes unseen before in herpetology. Male snakes carry ZZ chromosomes. Females carry ZW. When snakes had reproduced asexually before, they had created offspring with the same set. This female gave birth to WW snakes, something that was not considered possible.