Virgin births do occur among animals:
Many invertebrates, such as insects, can produce offspring asexually, without ever having mated. They usually do this by cloning themselves, producing genetically identical offspring.
But among vertebrate animals, it remains a novelty, having been documented among less than 0.1% of vertebrate species.
In 2006, scientists discovered that two komodo dragons (Varanus komodoensis), the world’s largest lizard species, had produced eggs that developed without being fertilised by sperm — a process called parthenogenesis.
Then in 2007, other scientists found that captive female hammerhead sharks (Sphyrna tiburo) could also reproduce without having sex.
Now researchers have discovered a female Boa constrictor that has produced two “virgin” litters — with an unusual chromosomal twist:
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.
So Dr Booth and colleagues conducted a series of genetic tests on the snakes to solve the enigma.
What they found was astonishing.
DNA fingerprinting revealed that the offspring had a number of genetic differences from any of their potential fathers, which ruled out all the males as sires of the litter.
That confirmed the first instance of a known virgin birth among boa snakes.
All the offspring also had very unusual sex chromosomes.
Sex chromosomes are packages of DNA that drive the development of sexual characteristics; they essentially make animals genetically male or genetically female.
Humans for example have X or Y sex chromosomes; females have two X chromosomes and males have a combination of an X and a Y chromosome.
In place of X and Y, snakes and many other reptiles have Z and W chromosomes. In all snakes, ZZ produces males and ZW produces females. Bizarrely, all the snakes in these litters were WW.
This was further proof that the snakes inherited all their genetic material from their mother, as only females carry the W chromosome. ”Essentially they are half clones of their mother,” says Dr Booth.
That is because the baby snakes have inherited two copies of one half of their mother’s chromosomes, including one W chromosome.