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: Ophthalmology
True about colour blindness: September 2005 
Select and explain. 
A. Autosomal dominant inheritance, B. Tritanopia is the commonest disorder, C. Trichromats are unable to appreciate blue colour, D. Defect in 1 or more prime colours
D: Defect in 1 or more prime colours
Answer: D: Defect in 1 or more prime colours 
Explanation: Ans. D: Defect in 1 or more prime colours Colour blindness is inherited as recessive and X-linked characteristics. The prefixes "Prot-" "Deuter-"and "Trit-" stands for defects of Red, Green and Blue cone systems. So tritanopia (Rarest) has Defect of blue colour. Trichromats are normal individuals.