PRA EXAMPLE

KEY
		~ Assumed normal
		~ Known to be a carrier
		~ Tested AFFECTED

To calculate the outcome, I have illustrated the best and the worst scenarios and then taken the "middle-of-the-road" (average) scenario. I agree that it is quite probable for some litters to produce mainly "best scenario" puppies but, on the other hand, the converse can also apply. It would, therefore, seem reasonable to work from the "middle-of-the-road" scenario.

Each dog is represented by a coloured square and each square has a value of 100%:

e.g. is NORMAL = 100% and is NORMAL = 25%, CARRIER = 50% and AFFECTED = 25%

Best scenario outcomes
for Glen X

"Middle-of-the-road" scenario outcomes
for Glen X
(See table and calculations below)

Worst scenario outcomes
for Glen X

Grandparents

Parents

GLEN X ...

Grandparents
Parents
GLEN X ...

The parentage of GLEN X is:		x
From GLEN X's parentage:
~ best scenario: NORMAL (from the sire's side) x CARRIER (from the dam's side) ~ worst scenario: CARRIER (from the sire's side) x CARRIER (from the dam's side)		&
To work out the odds for GLEN X "Add up the colours" (for best and worst scenarios) and then divide by 2:
~ NORMAL is 75 ÷ 2 = 37½% ~ CARRIER is 100 ÷ 2 = 50% ~ AFFECTED is 25 ÷ 2 = 12½%	~ GLEN X

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TABLE "A"	TABLE "B"	TABLE "C"	TABLE "D"	TABLE "E"	TABLE "F"
Normal x Normal	Normal x Carrier	Normal x Affected	Carrier x Carrier	Carrier x Affected	Affected x Affected

TABLE "A" - Normal x Normal

				Each puppy has a ...
				100% chance of being normal

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TABLE "B" - Normal x Carrier

				Each puppy has a ...
				50% chance of being a carrier

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TABLE "C" - Normal x Affected

				Each puppy has a ...
				100% chance of being a carrier

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TABLE "D" - Carrier x Carrier

				Each puppy has a ...
				50% chance of being a carrier 25% chance of being affected

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TABLE "E" - Carrier x Affected

				Each puppy has a ...
				50% chance of being a carrier 50% chance of being affected

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TABLE "F" - Affected x Affected

				Each puppy has a ...
				100% chance of being affected

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