Of course that is not true, your great grandpas were human. However, it has been known for a while that big chunks of your DNA is from viruses. Retroviruses such as HIV reproduce themselves by copying their genetic material, which is actually in the form of RNA not DNA,  into DNA which is then incorporated into your DNA. Then your cell’s machinery then copies the viruses DNA for it. Cunning. However sometimes things might go wrong, maybe a mutation, and the viral DNA can get stuck. If this DNA ends up in a sperm or egg the baby will have the viral DNA as part of the DNA in all its cells – it has a virus as a kind of an involuntary DNA-donor Dad. And in turn it will pass the viral DNA on to its children.

Anyway, thanks to an entertaining blog post by a PhD student called Abbie Smith who works on this sort of DNA, I now know why white (but not albino chickens) are white. All I have to do now is work out if white chickens always lay white eggs and my white-chicken knowledge will be complete.

A virus called the Avian Leukosis Virus has parked thousands of base pairs of DNA right in a gene which is essential for producing pigments. This appears to prevent production by the chicken of pigment in its skin, so its white. Simple. A nice piece of work by Chang et al. The chicken’s great, great, …, grandfather or grandmother caught a virus and as a result the chicken is white. Now all I need to do is work out what determines the egg colour ….