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    Default Genetics

    I've just finished a fascinating book called 'The Emperor of All Maladies', which is described as a biography of cancer (I like to know about things!). The later chapters, describing the genetic research into cancers, are particularly fascinating (though I think I understood about half of what I was reading!). They have discovered 'pathways' into cell activity that control how the cells behave. These pathways act differently in different cancers, but one of the components is responsible for switching on and off cell reproduction. In other words, the normal procedure tells the cell 'OK, you've done your job, now stop reproducing' and switches off that part of the cell. In cancers, the off switch gets jammed by a genetic mutation and the cells continue to multiply. Reading this, I thought (as a single-minded dog owner!) 'Chiari Malformation!'. Because this seems to be what happens in a Cavalier foetus and newborn: the off switch for the bone cells in the skull works OK, but the off switch for the brain cells doesn't work - at least not so quickly. So could CM be caused by a genetic mutation? In cancer cells, genetic mutation happens frequently - the cells refuse to die at their usual age and instead wriggle/mutate madly to avoid destruction and interference; so far no one knows why or how they mutate. So CM could simply have been caused decades ago by a mutating gene that then got passed down the generations. (In the same way that my wonky legs are possibly caused by a disease that is an inherited genetic mutation - when and how did that get into our family??)

    I'm probably talking rubbish, but the book did open up some interesting possibilities - besides making me very glad that I didn't have cancer 50 years ago!

    Kate, Oliver and Aled

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    Quote Originally Posted by Kate H View Post
    ... So could CM be caused by a genetic mutation? ... So CM could simply have been caused decades ago by a mutating gene that then got passed down the generations. ...
    I think that is what the current genetic research into CM is all about, finding those mutated genes.
    Rod Russell

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    I thought so, but this has interesting implications. Whatever caused the initial mutation (and we shall probably never know), it presumably has little to do with changing head shape, shorter muzzles and all the other possible external causes that some blame on breeders. Though it probably has to do with the small initial gene pool which meant that close inbreeding was more or less unavoidable, but which was continued through later generations, when it was avoidable but what everyone did in almost all show breeds (and cattle and sheep as well). It must be so exciting (and frustrating) to be a genetics researcher!

    Kate, Oliver and Aled

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    Quote Originally Posted by Kate H View Post
    ... Whatever caused the initial mutation (and we shall probably never know), it presumably has little to do with changing head shape, shorter muzzles and all the other possible external causes that some blame on breeders. Though it probably has to do with the small initial gene pool which meant that close inbreeding was more or less unavoidable, but which was continued through later generations, when it was avoidable but what everyone did in almost all show breeds (and cattle and sheep as well). It must be so exciting (and frustrating) to be a genetics researcher!
    A lot of purebred dogs' genetic disorders are not due to any gene mutations at all. Instead, they are due to a multiplier effect of line breeding.

    Kate, you mention "changing head shape, shorter muzzles and all the other possible external causes that some blame on breeders". Those are the exact things we can blame on breeders, and in some breeds, those sought-after features are the causes of the health problems. Like shorter muzzles causing brachycephalic heads and resulting breathing disorders.

    And don't blame the cattle and sheep farmers. Most of them have enough sense to borrow bulls and rams for matings. We did that on the small farm where I spent summers a very long time ago. There is nothing new to this strategy. It just is being ignored by a lot of purebred dog breeders.
    Rod Russell

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    But aren't we talking about two different things here? The genetic mutation that causes CM came into the breed long before head shape changed and muzzles shortened. These physical changes may have produced their own diseases and health problems, but they are not the cause of CM - as some have claimed - even if they make life more difficult for dogs with CM.

    I think what I found exciting about the genetics was that people speak about 'lack of communication' between the skull cells and the brain cells. But do cells communicate like that, or are we looking at one cell pathway that behaves normally (the skull development) and a different one that delays turning off the switch in the cells (in the brain)?

    I did say show breeders for cattle and sheep - not forgetting the breeding that was done in this country (and others) to increase milk yield, which can hardly be called good husbandry!

    Kate, Oliver and Aled

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    Quote Originally Posted by Kate H View Post
    But aren't we talking about two different things here? The genetic mutation that causes CM came into the breed long before head shape changed and muzzles shortened. These physical changes may have produced their own diseases and health problems, but they are not the cause of CM - as some have claimed - even if they make life more difficult for dogs with CM.

    I think what I found exciting about the genetics was that people speak about 'lack of communication' between the skull cells and the brain cells. But do cells communicate like that, or are we looking at one cell pathway that behaves normally (the skull development) and a different one that delays turning off the switch in the cells (in the brain)? ...
    Yes, I am referring to two different things, as you write.
    Rod Russell

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