In: Biology
Phenylketonuria is a recessively inherited disease. A woman and her husband do NOT have the disease yet their daughter has the disease. If the couple has a total of 3 children how likely is it: that all 3 children will have the disease? and that at least one child will NOT have the disease? (PLEASE INCLUDE LEGENDS, PUNNET SQUARES and show work)
Answer: Phenylketonuria (PKU) is an autosomal recessive disease due to mutation of the PAH gene located at 12q24.1. The normal function of this gene to synthesise protein enzyme that is phenylalanine hydroxylase (PAH). This PAH enzyme hydroxylates phenylalanine to tyrosine. Since it is an autosomal recessive disease so disease appears in the presence of homozygous defective alleles of this gene.
If the child of any couple is suffering from this disease and they do not have the disease means they are the carrier of this disease. For genetics and the combination of all the possible sets of the gene, only one is affected by this disease out of 4 from their carrier parents (see detail in figure below).
So it is not possible that all three children’s will be affected by this disease. The resultant probability for the occurrence of all three children is (0.25)3. That is 0.0156%.
So 0.0156% is the chance for occurrence of all three children suffering from this disease. Not the chance for the occurrence of the disease is 1- 0.0156 = 0.98%.