. Phenylketonuria is caused by a mutation in the gene encoding the enzyme phenyl

Question

. Phenylketonuria is caused by a mutation in the gene encoding the enzyme phenylalanine hydroxylase (PAH). The mutation results in the accumulation of phenylalanine which, in turn, causes damage to the developing nervous system and is manifested in severe m retardation. If a person is homozygous for the mutated form of the PAH gene, phenylketonuria develops, but if the person is heterozygous for PAH (one allele normal, the other mutated) he or she will not develop the disease. Sophie and her husband are both heterozygous for the PAH gene. Sophie is pregnant with twins. What is the probability that both twins will develop phenylketonuria if they are fraternal (non- identical) twins? What is the probability that they both develop phenylketonuri are identical twins? ental if they

Explanation / Answer

Ans: Phenylketonuria is a recessively inherited disorder. Causes one to be unable to break down amino acids, which leads to intellectual disability. If it is detected during infancy, steps can be taken to prevent it. phenylketonuria causes a baby to have problems digesting the amino acid phenylalanine. White babies are more at risk for it. Families need to make sure that if their baby has the genotype for it their baby consumes no foods containing phenylalanine.

Identical twins (monozygotic twins): Twins who develop from a single fertilized egg that splits in two, creating two genetically identical organisms

Fraternal twins (dizygotic twins): Twins who develop from separate fertilized eggs. They are genetically no closer than brothers and sisters, but they share a fetal environment.

P = PKU normal (no PKU)

p = disease with PKU

Parents Pp x Pp

F1 ¼ PP   ½ Pp    ¼ pp    phenotypes are ¾ normal and ¼ disease with PKU

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