Phenylketonuria (PKU) is a disease that results from a recessive gene. Two normal parents produce a child with PKU.
What is the probability that a sperm from the father will contain the PKU allele?
What is the probability that an egg from the mothe contain the PKU allele?
1/2
2/3
2/3
3/4
1/3
1/4
3/4
1/2
1/4
The Correct Answer and Explanation is :
Phenylketonuria (PKU) is a genetic disorder caused by a recessive allele. To understand the probabilities of the parents passing on the PKU allele, we need to explore the genetics behind this condition.
PKU is inherited in an autosomal recessive manner, which means that a person must inherit two copies of the PKU allele (one from each parent) to express the disease. A person with the genotype “aa” has PKU, while a person with the genotype “Aa” is a carrier (heterozygous), and a person with the genotype “AA” does not have the disease and is not a carrier.
In this case, we are told that both parents are normal but have a child with PKU. This means that both parents must be carriers of the PKU allele (genotype “Aa”), because two carrier parents (both heterozygous) can have a child with PKU (aa).
To determine the probability of a sperm or egg containing the PKU allele:
- Father’s sperm:
The father has the genotype “Aa,” meaning he carries one copy of the PKU allele (a) and one normal allele (A). The probability of a sperm cell containing the PKU allele (a) is 1/2, as half of the sperm will carry the “A” allele and the other half will carry the “a” allele. - Mother’s egg:
Similarly, the mother also has the genotype “Aa.” Half of her eggs will carry the “A” allele, and half will carry the “a” allele. Thus, the probability of an egg containing the PKU allele (a) is also 1/2.
Conclusion:
The probability that a sperm from the father will contain the PKU allele is 1/2, and the probability that an egg from the mother will contain the PKU allele is also 1/2.
Therefore, the correct answer to both questions is 1/2.