Question

In humans, PKU (phenylketonuria) is a disease caused by an enzyme inefficiency at step 1 (diagram above), and AKU (alkaptonuria) is due to an enzyme inefficiency in step 4. Both mutant alleles are recessive to the respective wild type allele, and the genes involved are located on different chromosomes.

A person with PKU marries a person with AKU. What phenotypes do you expect for their children?

Justify by providing correctly written genotypes for both parents and potential offspring.

Answer 1

In autosomal recessive inheritance, two copies of a disease allele are required for an individual to be susceptible to expressing the phenotype.

Normal/PKU=P/p

Normal/ AKU=A/a

Scenario 1:

ppAA(person with PKU) x PPaa (person with AKU)

=PpAa

All the children would be healthy but carry a recessive alleles of both genes

Scenario 2:

ppAa(person with PKU) x Ppaa (person with AKU)

	Pa	pa
pA	PpAa	ppAa
pa	Ppaa	ppaa

1 Healthy carrier

1 AKU

1 PKU

1 both PKU and AKU

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