This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
An affected male infant born to normal parents could be an example of all of the following, except: 
Select and explain. 
A. An Autosomal dominant disorder, B. An Autosomal recessive disorder, C. A polygenic disorder, D. A veically transmitted disorder
A: An Autosomal dominant disorder
Answer: A: An Autosomal dominant disorder 
Explanation: A i.e. Autosomal dominant disorder Autosomal dominant disease cannot occur in offspring of an unaffected individuals. Because the allele is dominant it will always express phenotypically (clinically) and hence both parents can't be normal in autosomal dominant disorders even if they have a single abnormal gene.