Question

Which of the following has normal vision?
A. $X^CX^C$
B. $X^c$Y
C. $X^CX^c$
D. $X^cX^c$

Answer 1

Hint: X- linked traits in the human body are mostly recessive that is they only express their characters when they are present in the recessive state. In the dominant state, they show the normal property.

Complete answer:
The X- linked traits in the human body are mostly recessive and one of such examples of the X-linked recessive disease found in humans is the Colour-blindness disease. It is associated with the X – chromosome and expresses its characters in the recessive state. Thus, $X^c$ represents the recessive allele that causes colour-blindness and $X^C$ represents the dominant allele that is a normal condition.
Hence, the females, those who are $X^CX^C$ or $X^CX^c$ have normal vision. Whereas, the females having $X^cX^c$ chromosomes, are colourblind.
In the case of males, $X^c$Y is colourblind.
In the given options, Option A is correct. Because the chromosome set up shows dominant characters.
Option B is incorrect since $X^c$Y is for the male chromosome set which has an X-chromosome linked to the recessive trait.
Option C is incorrect because the genotype shows the dominant character.
Option D is incorrect because the $X^cX^c$ genotype causes colour-blindness and does not have a normal vision.

So, the correct answer is “Option A”.

Note:
Colour blindness is an X-linked recessive disease. Thus when the chromosome is present in the homozygous recessive condition, then only the gene will be expressed and show colour blindness. In other cases, like homozygous dominant state and heterozygous condition, the gene won’t express itself thus, even the X carries the factor for the colourblind, will have normal vision.