A couple with normal vision bear a colour blind child. Work out a cross to show how it is possible and mention the sex of the affected child. - Biology

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A couple with normal vision bear a colour blind child. Work out a cross to show how it is possible and mention the sex of the affected child.

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Solution

Colour blindness is an X-linked recessive disease.

Condition: 

Male:  XY - Normal
         XcY - Colour-blind

Female: XX - Normal
            XcX - Carrier
            XcXc - Colour blind

According to the given situation, both the parents are normal but the child is colour blind. This means that the male parent is normal and the female parent is the carrier. The cross can be represented as follows:
 
Parents        XY      ☓      XcX
Gametes      X,Y             Xc,X

Offsprings    XcX    XX     XcY    XY

Result: 50% sons are colour blind.
Thus, the affected child will be male.

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2015-2016 (March) Delhi Set 2

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