Ginger cats have gained a reputation for being slightly dim but very loveable agents of chaos. Whether or not this is true is still up for debate, but ginger cats are unique for another reason.
Red headedness isn’t rare in the animal kingdom. Think of humans, orangutans, foxes, tigers and golden retrievers. But in all these species, being ginger is not more common in males or females.
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In cats, however, ginger individuals are usually male. This means that while in most redheaded mammals the genetic basis for ginger colouration is nothing to do with sex chromosomes, it is in cats.
Cats, like all mammals, have two sex chromosomes per cell – one inherited from the father and one inherited from the mother. While males have one X and one Y chromosome, females have two X chromosomes.
In each cell, only one X chromosome needs to be active, so in females one X chromosome gets turned off at random. This means that if females inherit DNA that encodes ginger fur on one X chromosome but not on the other, they will have a patchwork appearance of ginger and other fur colours. These cats are what we call tortoiseshell or calico, and they are almost always female.
Meanwhile, male cats who inherit a ‘ginger X chromosome’ are completely ginger, because they have only one X chromosome and therefore no alternative fur colours in their genetic code.
But what we have not known until now is where on the X chromosome ginger fur is actually encoded.
Finding the missing link
In a new study, Stanford Medicine researchers solved this mystery by examining feline X chromosomes using the latest genomic techniques.
By looking in detail at the DNA of ginger, tortoiseshell, calico and non-ginger cats, the team discovered that ginger fur is caused by a missing segment of DNA on the X chromosome. This missing DNA causes a nearby sequence of DNA in the X chromosome – a gene called Arhgap36 – to be ‘turned on’ in pigment cells, where it would usually be inactive. It is this gene’s activity in pigment cells that causes ginger fur.
The scientists are now interested in exploring whether this DNA deletion might be linked to characteristics beyond fur colour, such as health and perhaps even personality.
Find out more about the study: A deletion at the X-linked ARHGAP36 gene locus is associated with the orange coloration of tortoiseshell and calico cats.
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Main image: an orange tomcat. Credit: Getty
