For the most part, snakes reproduce sexually, with males carrying two Z sex chromosomes and females one Z and one W. Warren Booth of North Carolina State University in Raleigh and his colleagues have identified an unprecedented natural occurrence of WW females born to a single female Boa constrictor imperator.
By analysing the DNA of the female and two of her broods that were all-female, the researchers ruled out sexual reproduction with cohabiting male boas. However, the offspring were not clones of their mother, and the authors suggest that they were the result of automictic parthenogenesis. In this form of reproduction, the egg's nucleus fuses with another cell structure in the egg that carries half of the mother's chromosomes.
This is the first evidence of multiple, viable and non-experimentally induced WW females in a vertebrate, the authors say.