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PRA3 Probability Chart

PRA probablility chart.jpg.jpeg

Certainty of PRA3 in Tibetan Spaniels

The chart above illustrates the three following statements:

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For the time being, the only “certainties” regarding PRA in Tibetan Spaniels are:

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  1. If a Tibetan Spaniel is tested Affected, its sight will deteriorate and it will eventually be blind.

  2. If a Tibetan Spaniel is tested Affected, then both its parents must (at least) be Carriers i.e. the result of (carrier x carrier) or (carrier x affected) or (affected x affected) matings.

  3. If a Tibetan Spaniel is tested Affected, then all its progeny will (at least) be carriers.

Offspring of an affected parent are always carriers or affected depending on the other parent. Offspring of a known carrier have a 50% probability of being carriers if the other parent is genetically normal. Grandchildren of a known carrier have a 25% probability of being carriers. (These probabilities apply only over large numbers, and will not necessarily apply to a specific litter.)

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