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Multiple Choice
In a family where the father has hemophilia (an X-linked recessive disorder) and the mother is a carrier, what is the probability of their daughter having hemophilia?
A
50%
B
25%
C
0%
D
0%
Verified step by step guidance
1
Understand that hemophilia is an X-linked recessive disorder, meaning the gene causing hemophilia is located on the X chromosome and two copies of the recessive allele are needed for females to express the disorder.
Identify the genetic makeup of the parents: The father has hemophilia, so his genotype is XhY (where Xh represents the X chromosome with the hemophilia allele). The mother is a carrier, so her genotype is XHXh (where XH represents the normal X chromosome).
Determine the possible genotypes for their daughters: Daughters receive one X chromosome from each parent. Therefore, the possible combinations are XHXh (carrier) and XHXh (carrier).
Recognize that for a daughter to have hemophilia, she would need to inherit two Xh chromosomes. However, since the father can only pass on a Y chromosome to sons and an Xh chromosome to daughters, and the mother can pass either XH or Xh, the daughter cannot inherit two Xh chromosomes.
Conclude that the probability of their daughter having hemophilia is 0% because she cannot inherit two Xh chromosomes from her parents.