A Basic Explanation on Why (Almost) All Tortoiseshell Cats Are Female – with Walter Bodmer


Now, I wonder whether you’ve ever seen a tortoiseshell
cat. Here we’ve got one. Binny is her name, isn’t it? – Bonnie. Bonnie. Bonnie. Here we’ve got… and isn’t
she lovely? Isn’t she lovely? And she’s a very good cat.
She’s been waiting all day for this. I don’t think she’s going to go away. And you see that she’s a patchwork. Isn’t
she? She’s a patchwork of black and yellow. And her parents were probably, I don’t know, maybe one of them was black and one was slightly
brownish. She’s a really lovely cat, I’d better give
her back to you. She’s getting a bit worried here. There’s a patchwork there of both types of
colours of fur. And you can have patchwork mice too. Bill,
let’s have a look at these patchwork mice. Look here, we’ve got some mice here. And here
you see the one of the parents is black. The other is white. And here we have the offspring. Look, you
see they are patchwork. Can you see that? Both of them. Both of them are patchwork of
black and white fur. They are patchwork just like the cat. The tortoiseshell cat. The tortoiseshell cat’s a female. And these
are females. They’re always patchwork females, not patchwork
males. Now why do you think that is? The reason for that is, in the sex chromosomes
again, the X and the Y. Remember, two X’s in the female. One X and
a Y in the male. And you see the Y’s a little chromosome. It only determines sex basically, whether
you’re a male. There isn’t, as there is for the other chromosomes,
which occur in pairs like that, a matching set of genes in the male for the
X’s. There’s only one set of X genes not too set
of X genes. Now, nature doesn’t like that sort of imbalance. Nature tries to arrange it so that the number
of active X chromosomes, the number that’ll work in every cell, is
the same. There’s only one in the males. What happens in the females is either one
is at work or the other. Never both chromosomes at work. So if one of those chromosomes determines
the black colour. The X chromosomes. And the other X chromosome determines the
white colour. You get this patchwork. Some have one of the
X’s that work, and some have the other of the X chromosomes
at work. And that’s why you get a patchwork in the
females and not in the males.

15 thoughts on “A Basic Explanation on Why (Almost) All Tortoiseshell Cats Are Female – with Walter Bodmer

  1. We have a sprinkling of piebald deer here where I live. Does this apply to piebald animals or is this a different phenomena?

  2. My Jazzie has a perfect line in the middle of her face, the left side is yellow and right is black so my friends like to call her Tony Twoface 😛 And she acts like she has a split personality as well, super sweet or Speedy Gonzales 😀

  3. I understand this occurs in human females as well (having different X chromosomes active through their bodies) but it doesn't seem to affect hair color.

  4. We had a male tortoiseshell cat. But it had lost the ball race with a vet, before it adopted us. Someone wasted their money on an already sterile cat

  5. I am concerned by how the mouse is picked by the tail. Never pick any non prehensile tailed animal, by their tail.

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