BR bio, section V, passage VIII, question 51

[Student1331]

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BR bio, section 5, passage 8, question 51

Question: Hypophosphatemic rickets is an X-linked dominant trait that leads to decreased levels of phosphate reabsorbtion in the kidneys. Which pedigree shown below BEST represents this disease?

 

[MedPR]

BR bio, section 5, passage 8, question 51

Question: Hypophosphatemic rickets is an X-linked dominant trait that leads to decreased levels of phosphate reabsorbtion in the kidneys. Which pedigree shown below BEST represents this disease?

Which part are you having trouble with?

X-linked dominant means that every daughter and no son of an affected father will have the disease. If you didn't know the shortcut, you can do it a longer way.

If the mother isn't affected, then none of her sons can have it since the son gets his X from the mother and the Y from the father. This means that answer A is out.

Answer B is wrong for a similar reason. In X-linked dominant, two unaffected parents cannot have an affected child.

I don't know if you can rule out D without knowing the fact that X-linked dominant is indicated by all daughters and no sons of an affected men are affected.