Block 7 Repro Bayes Questions MCQ's

Explanation
Prior risk 1/2 then chance of having normal child 1/2. Because she had 3 normal it is 1/8.
so then 1/2 x 1/8 gives 1/16, the other colum give 8/16 so 1/16/(1/16)+(8/16) gives 1/9

Explanation
Based on the information given, it is stated that two brothers have classical hemophilia. Classical hemophilia is an X-linked recessive genetic disorder, which means it is carried on the X chromosome. Since the two brothers have hemophilia, it can be inferred that their mother must be a carrier of the gene. Therefore, the chance of the mother being a carrier is 50%. However, since the question specifically asks for the chance of her being a carrier, we need to consider that she has two healthy sons. This information reduces the probability by half, resulting in a 20% chance of her being a carrier.

Explanation
prior risk of 1/2, you have a 1/3 chance of being normal if you carry the gene. therefore you multiply your prior risk of 1/2 by 1/3 to give you 1/6 (so you know that is not the final answer) then the right colum is 3/6. so divide the 1/6 by the sum of 1/6 and 3/6 to give you 1/4.....ta da!!!!!

Explanation
Based on the information provided, it states that two-thirds of all patients who carry the Huntington's gene show signs of the disease by age 45. However, the patient in question is still healthy at 45 years old. This suggests that the patient falls into the one-third of individuals who do not show signs of the disease by this age. Therefore, the likelihood of the patient getting the disease can be estimated as 1 in 4.

Explanation
moms risk is 1/5 therefore her risk is 1/2 of that.

Explanation
Michael's risk is 1/6 so multiply by 1/2 (chance of passing the gene) and 4/5 (penetrance)
1/6 x 1/2 x 4/5 = 4/60= 1/15

Explanation
Based on the information given, Sydney's paternal grandfather had Huntington disease (HD), her father is unaffected, and her brother was diagnosed with HD at the age of 32. It is mentioned that approximately 10% of HD gene carriers are clinically affected by the age of 30. Therefore, Sydney has a 10% chance of developing HD by the age of 30. The answer 9/19 suggests that Sydney has a higher chance (9 out of 19) of developing HD by the age of 30, based on the given statistics.

Explanation
__________Both Carriers___________ Not Both Carriers_____________
Prior.............1/25 x 1/2=1/50.....................1 - 1/50=49/50
Conditional ....(3/4)2=9/16 ......................................16/16
Joint .........................9/800...................................784/800
Posterior....................9/793 (= ~1/88*)..................784/793
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risk of having an affected child therefore is 1/88 x 1/4 = 1/352

Explanation
The chance that Jane's fetus will be affected is 1/22. This is because the question states that Jane's brother died of severe X-linked hydrocephalus, which implies that he was affected by the condition. Since Jane has two unaffected brothers, it is likely that her mother is a carrier of the X-linked gene. The chance of Jane being a carrier is 2/3, and since she already has one unaffected son and one unaffected daughter, it is likely that she is a carrier. Therefore, the chance of Jane passing on the affected gene to her fetus is 1/2, and the chance of the fetus being affected is 1/2 x 2/3 x 1/2 = 1/6. However, the question also states that 1/3 of isolated cases are new mutations, so the chance of the fetus being affected by the inherited gene is 2/3 x 1/6 = 1/22.

Explanation
_________________Carrier____________ Non-Carrier
Prior..............................2/3 ................................1/3
Conditional #1 .............3/10.............................10/10
Conditional #2 .............1/2............................... 2/2
Joint ............................6/60 ...........................20/60
Posterior ....................6/26=3/13* .................10/13

3/13 x 1/2 = 3/26

Explanation
Based on the information provided, the chance that Carol's next child will have DMD is 3/92. This can be inferred from the fact that Carol has a son with DMD and there is no other family history of the condition. The woman's normal CPK levels also suggest a lower likelihood of being an obligate carrier. Therefore, the chance of having a child with DMD is relatively low, resulting in a probability of 3/92.

Explanation
________________Both Carriers_______________ Not Both Carriers_______
Prior ..........................1/25 x 2/3=2/75..........................1 - 2/75=73/75
Conditional ........................3/4 .....................................................4/4
Joint ..................................6/300..............................................292/300
Posterior ...........................6/298 (= 3/149) ..............................292/298
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risk of having an affected child therefore is 3/149 x 1/4 = 3/596
approximately 1/199