question: Q:A 24-year-old man comes to the physician because his vision has worsened rapidly over the last 2 months. His maternal uncle lost his vision suddenly over a period of 3 months at 26 years of age. The patient's wife and 1-year-old son have normal vision. Funduscopic examination of the patient shows bilateral circumpapillary telangiectasia. Genetic testing shows a missense mutation in one of the genes of the electron transport chain complexes. The probability that this patient's son will be affected by the same disease is closest to which of the following?? 
  {'A': '0%', 'B': '25%', 'C': '33%', 'D': '50%', 'E': '100%'},