A couple with normal vision has a child with colour blindness. Since we know that colour blindness is an X-linked disease, how would you indicate the mother in the pedigree chart?
With a circle that has 50% shaded area
In the mentioned case, the mother would be a carrier of colour blindness. A person who is a carrier for a certain genetic disorder is not affected by it. To signify that the female parent is a carrier of the defect, a circle that has 50% shading is used in the pedigree chart. So the correct indication here will be a circle with 50% of its area shaded, indicating that one of her X chromosomes carries the defective allele, and the other X chromosome has a normal allele.