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Divya_4978
#1 Posted : Saturday, July 11, 2020 3:30:05 AM
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Hello,

I was working on the practice set 4 for biochem and I encountered a genetics question which I did not understand.

Question is from Passage 9 number 50.

The question asks: " There is another form of hypercholesterolemia is determined by an autosomal recessive trait that results in high concentrations of LDL cholesterol in the blood. A man who is affected but has 3 unaffected siblings and one affected parent for the dominant allele marries a woman who is affected by the recessive version of the trait. What is the probability that they will have an affected child?

I understand the man is heterozygous (Aa) and the affected wife is recessive (aa) however I do not why the probability that they will have an affected child is 1/2.

Thank you in advance.
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INSTR_Katerina_102
#2 Posted : Monday, July 13, 2020 6:02:33 PM
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Hi Divya,

I cannot find the original question myself so I will go off of your statments.

From what I understand, the trait is autosomal recessive so only

aa = high LDL concentrations in blood (phenotype)

aa is the genotype that will result in an affected child.

As the man has Aa and his wife has aa, we would draw a punett square:

Aa x aa

Aa ||aa
Aa ||aa

2/4 or 1/2 of the expected genotypes are aa, which is the affected phenotype.

Therefore we would expect the probability of an affected child to be 1/2.

Please let me know if I have misunderstood the question or if something is unclear.

Katt
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