"The female [boa] has had not one virgin birth, but actually two, in spite of being housed with and observed to be courted by multiple males. "All offspring are female. The offspring share only half the mother's genetic make-up..."More at the BBC.
First impressions suggested there was something special about these babies: all were female and all had a particular, rare caramel colouration. This colour is a rare recessive genetic trait, which is carried by the mother but not by any of the potential fathers... the baby snakes have inherited two copies of one half of their mother's chromosomes, including one W chromosome.
One other mystery is what prompted the female snake to give birth this way. "This female has given birth to sexually produced babies in the past, and only in years that she was housed with males has she produced offspring," Dr Booth explains. "It appears that some interaction with a male is required.
"However, why she does not utilise his sperm is at present unknown."