Question 1: Imagine that you have developed a genetic test to detect the dominan

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Question 1: Imagine that you have developed a genetic test to detect the dominant allele (A) that cause a rare genetic condition. As with most clinical tests, it isn't perfect. When a person does have the dominant allele (Aa or especially rarely AA) your test detects it 100% of the time. But, 0.5% of people who are homozygous recessive (aa) also test positve by your test.

Assume 1 out of every 100 people in a population has the dominant allele (Aa or AA).

Part A - What percentage of the population will give a positive test? Choose one only.

1.495%

1.000%

99.505%

99.000%

0.495%

98.505%

Part B - If a person tests positive, what is the probability that they actually have the dominant allele (AA or Aa)? Choose one only

0.111

1.000

0.331

0.005

0.889

0.669

Question 2: Mike and Stephanie are first cousins. Their common grandfather had a rare autsomal recessive condition.

Part A - What is the probability that both Mike and Stephanie are carriers for this rare autosomal recessive condition at the same time? Answer in fraction form.

Part B - What if Mike and Stephanie have a child together and that child does not show the condition. Given this new information, what is the probability that both Mike and Stephanie are carriers for this rare autosomal recessive condition at the same time? Answer in fraction form.

Explanation / Answer

Part A.

Option A is correct.

1 person is AA or Aa out of 100.

99 people are recessive. But, 0.5% of 99 = 0.495% will show positive result.

So, total positives = 1 + 0.495 = 1.495%

Part B.

Option E is correct.

There is a 100% possibility for positive result if a person is AA or Aa

There is a 0.5% possibility for positive result if a person is aa

Q2.

Assumption: all other individuals are AA

Common grandfather = aa

Grandfather's progeny must be = Aa (assuming his wife to be AA)

Mike's parents: Aa X AA

The probability that Mike is a carrier = 1/2

Stephanie's parents: Aa X AA

The probability that Stephanie is a carrier = 1/2

The probability for both of them to be carrier at the same time = 1/2 X 1/2 = 1/4

Mike and Stephanie: Aa X Aa

Progeny: AA Aa Aa aa

There is 1/4th chance that their child is affected if both Mike and Stephanie are carriers.

There is 1/4th chance that their child is WT homozygous if both Mike and Stephanie are carriers.

There is 1/2th chance that their child is a carrier if both Mike and Stephanie are carriers.

If Stephanie and Mike are not carriers,

AA X AA

Progeny: AA

There is no chance that their kid to be affected.

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