Question

In protanopia, a person cannot distinguish
A. Green colour
B. Red colour
C. Blue colour
D. Blue and green colour

Answer 1

Hint: Colour blindness is a recessive sex-linked trait in which the eye fails to distinguish red and green colours. Colour blindness shows criss-cross inheritance. It is of three types:
> Anomalous Trichromacy
> Dichromacy
> Monochromacy

Complete answer:
Colour blindness is a genetic disorder. It is most commonly caused by the mutations on the X-chromosome. The gene for normal vision is dominant. The normal gene and its recessive allele are carried out by X-chromosome. It is a disease in which people have trouble seeing the differences between certain colours.
Eyes are a very important organ of the human body and it contains rods and cones in each eye which are responsible for the vision in dim light and bright light. The most common cause of colour blindness is the less development of cone cells present in the eyes which sense colours. Rods and cones are the photoreceptors in the eyes which detects light.
Protanopia falls under the category dichromacy of the disease colour blindness.
People with dichromatic colour vision have only two types of cones which are able to perceive colour and dichromacy is hereditary. People with protanopia are unable to see any red colour because they only perceive light of wavelength 400 nm to 650 nm.
Those people who are unable to see green colour are suffering from deuteranopia.
Those people who are unable to see blue are suffering from tritanopia.

So the correct answer is option B.

Note: The chances of this disorder in females are very less and it appears only when both the sex chromosome (XX) carry the recessive gene but in males the defect appears in the presence of a single recessive gene because Y-chromosome of males do not carry any gene for colour vision.