Diagram for inheritance of PRA (Progressive Retinal Atrophy)

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reproduced with kind permission from Swedish Siamese Society (SES)


PRA is a hereditary eye disorder where the retina slowly degenerates, making the cat blind. This page illustrates the inheritance.


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= Normal - cat without the gene for PRA, does not pass on the gene for PRA


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= Carrier - cat with one gene for the disorder, can pass this gene on to progeny, will not develop PRA


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= Affected - cat with two genes for the disorder, will pass this gene on to progeny, will also develop PRA


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Normal cat mated with normal cat

100% of the progeny will be normal/without the gene for PRA

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Normal cat mated with carrier

50% will be carriers, 50% will be normal

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NB! The following combinations are not recommendable and should not be done

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Carrier mated with carrier

25% of the progeny will get PRA, 50% will be carriers and 25% will be normal

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Carrier mated with affected cat (has PRA)

50% of the progeny will be affected and 50% will be carriers

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Affected cat mated with normal cat

100% of the progeny will be carriers

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Affected cat mated with affected cat

100% of the progeny will be affected

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