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Question

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?


A

With a circle that is completely shaded

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B

With a circle that has 50% shaded area

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C

With a completely shaded circle and a diagonal line across it

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D

With a completely shaded circle and a horizontal line below it

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Solution

The correct option is B

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.


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