Today the conversation turned to cat genetics and the extent to which cats look like their parents. I thought of lanfykins and some of the things she'd said on the subject.
We were in general agreement that tortoiseshells were always female. R - whose girlfriend works for a cat rescue charity (and they usually have several of the patients at their flat at any one time) - commented that he'd seen lots of tortoiseshells and they were all female.
However, none of us knew why. So - yes - when you have a spare hour (however long it takes) I might send it on to work.
It's because cats have more different genes for colour than any creature could possibly require.
The gene that controls ginger is totally separate from all the other colour genes, and it only has two versions: 'ginger' or 'not ginger'. A cat always has two copies of every gene, so if it ends up with one ginger gene and one not-ginger gene, it ends up both ginger and not-ginger at the same time; or tortoiseshell.
The thing that complicates this is that the ginger gene is, for reasons best known to itself, on one of the sex-linked chromosomes (the X). So female cats, having two X chromosomes, can have both a ginger and a not-ginger version of the gene, making them tortoiseshell. But male cats only have one X chromosome (partnered by a Y chromosome) and so they can only have one version of the gene, and are always either ginger or not-ginger.
(It's possible for a male cat to be tortoiseshell, because sometimes cell division goes wrong and it ends up with three sex chromosomes (XXY), which could give it two versions of the gene. But that's a genetic abnormality that would also have some other effects, such as making it sterile)
Does that mean that female cats can be ginger, if they have two copies of the ginger gene? I wondered, because I think I've only ever seen male gingers.
Imagine a mating between a non-ginger (n) queen and a ginger (g) tom.
The queen will always donate a non-ginger allele, and the tom will always donate a ginger allele, so the resulting female kittens will all have a genotype of ng and therefore be tortoiseshell. (And all the male kittens will be non-ginger, because their father has donated his Y chromosome and therefore they get their X chromosome from their mother, with her non-ginger allele).
Doing the maths, the only way to get a ginger female is by mating a tortoiseshell or ginger female with a ginger tom. In the former case 1/3 of the females will be ginger, and in the latter case all of them will.
That all sounds right to me. Except half (not 1/3) of the females (and only half of the males) will be ginger if you mate a tortoiseshell female with a ginger tom.
I've met one! Melys - the mother of the late Smith and Jones, two of the cats I grew up with - was a ginger female. (Smith was a ginger male and Jones was a tortoiseshell female. If I recall correctly their father was thought to be the huge black pompom that liked to poo in my aunt's gooseberry patch.)
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timeasmymeasure
no subject
Date: 2010-12-14 10:23 pm (UTC)no subject
Date: 2010-12-15 07:45 am (UTC)However, none of us knew why. So - yes - when you have a spare hour (however long it takes) I might send it on to work.
no subject
Date: 2010-12-15 08:03 am (UTC)The gene that controls ginger is totally separate from all the other colour genes, and it only has two versions: 'ginger' or 'not ginger'. A cat always has two copies of every gene, so if it ends up with one ginger gene and one not-ginger gene, it ends up both ginger and not-ginger at the same time; or tortoiseshell.
The thing that complicates this is that the ginger gene is, for reasons best known to itself, on one of the sex-linked chromosomes (the X). So female cats, having two X chromosomes, can have both a ginger and a not-ginger version of the gene, making them tortoiseshell. But male cats only have one X chromosome (partnered by a Y chromosome) and so they can only have one version of the gene, and are always either ginger or not-ginger.
(It's possible for a male cat to be tortoiseshell, because sometimes cell division goes wrong and it ends up with three sex chromosomes (XXY), which could give it two versions of the gene. But that's a genetic abnormality that would also have some other effects, such as making it sterile)
Did that make sense?
no subject
Date: 2010-12-15 08:05 am (UTC)Yes - thanks. I may pass that on, if that's OK?
no subject
Date: 2010-12-15 08:11 am (UTC)no subject
Date: 2010-12-15 09:28 am (UTC)no subject
Date: 2010-12-15 10:08 am (UTC)Imagine a mating between a non-ginger (n) queen and a ginger (g) tom.
The queen will always donate a non-ginger allele, and the tom will always donate a ginger allele, so the resulting female kittens will all have a genotype of ng and therefore be tortoiseshell. (And all the male kittens will be non-ginger, because their father has donated his Y chromosome and therefore they get their X chromosome from their mother, with her non-ginger allele).
Doing the maths, the only way to get a ginger female is by mating a tortoiseshell or ginger female with a ginger tom. In the former case 1/3 of the females will be ginger, and in the latter case all of them will.
I think.
no subject
Date: 2010-12-15 11:36 am (UTC)no subject
Date: 2010-12-15 11:56 am (UTC)no subject
Date: 2010-12-15 12:17 pm (UTC)no subject
Date: 2010-12-15 11:48 pm (UTC)