This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetics And Genetic Disorders, Subject name: Pediatrics
In a family, mother is normal while father has a genetic disease. All their daughters are carriers and sons are normal, what is the pattern of inheritance of disease? 
Select and explain. 
A. X-linked recessive, B. X-linked dominant, C. AD, D. AR
A: X-linked recessive
Answer: A: X-linked recessive 
Explanation: a. X-linked recessive(Ref: Nelson's 20/e p 595, Ghai 8/e p 640)In a X-linked recessive disease; affected male transmits the disorder to all his daughters (carriers)Sons get their X chromosome from their mother & not from their fatherHence sons of a diseased father are unaffected in X-linked diseasesIn an X-linked dominant disorder all the daughters of an affected father would be diseased and not carriers.