Male tortoiseshell cats: like hens' teeth – Telegraph Blogs

Thursday 30 July 2015 | Blog Feed | All feeds

Pete Wedderburn


Male tortoiseshell cats: like hens' teeth


The coat-colour of cats is in the news today: a male tortoiseshell (white, orange and black) cat has turned up. The link between gender and coat colour in cats is interesting, and I’ve had experience of the consequences of this since I was a young child.

My first pet was a ginger kitten who arrived in my life when I was five years of age. She was named Honey, but when she was taken to the vet for spaying a few months later, we were informed that we’d been mistaken: “she” was a “he”.  It was too late to rename him, so he remained Honey until the day he died, and he was frequently referred to as a “she” as a consequence. Later on, I discovered that 75% of ginger cats are male, so we really ought to double checked his gender at an earlier stage, even if we were unfamiliar with assessing cats’ under-tail anatomy.

The genetics underlying coat colour in cats are interesting, and the clearest explanation of this that I’ve discovered is from Huw Rees at Notes and Queries across at the Guardian. His summary is well worth reading if you’re interested:

“All cats have 19 pairs of chromosomes, and like humans, cats have one pair of sex chromosomes. These are the ones that make them male or female and they play an essential role in determining their colour. In females, both sex chromosomes are X making females XX. Males are XY, the Y making them male. The gene which makes a cat ginger is located on the X chromosome. The gene for mighty ginger will override all other colours. Since males have only one X, they either are or aren't ginger. Female cats have two X's in each cell. As far as the cells are concerned two X's is one too many, so each cell deactivates one of the X chromosomes in a fairly random fashion. Sometimes the ginger X will be left on producing a bit of orange fur and in some cells the ginger X will be turned off and the genes for black, brown or other colour fur will be produced. And there you have Tortoiseshell Cat. Since males only need to have the orange gene on one chromosome to become ginger, and females have to have it on two, ginger males outnumber females 3 to 1. To show both orange and another colour such as black or brown a cat has to have two different X chromosomes per cell. Therefore tortoiseshell female cats outnumber males by at least 200 to 1, although I suspect actual figures are much higher. When a male tortie does appear (a result of a mutation producing two X’s and one Y), he is invariable sterile and may even exhibit feminine behaviour such as nurturing nearby young.”

So now you know. The male tortoiseshell cat is a rare beast who clearly has unusual genes. He’d be an ideal candidate for a novel form of wall art that’s recently become available: a massively enlarged image of your pet’s DNA. It’s easy to do: you send a mouth swab off to the company, and five weeks later, the “work of art” arrives on your doorstep. Perhaps it’s not for everyone, but if you’ve a male tortoiseshell cat, that rare DNA may just be worth preserving for posterity.

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