Question

Three Mark Questions :
A colourblind child is born to a normal couple. Work out a cross to show how it is possible.Mention the sex of this child.

Answer 1

Colour blindness is an X-linked recessive disorder. Therefore, since a male child has a single X chromosome, the child will show symptoms of the disease if the chromosome is affected. The couple if normal can transmit disease to the child only if the mother is a carrier of the disease. In this condition one of the X-chromosomes in the mother will be affected and the other will be normal. Due to this, she will not show symptoms of the disease. However, she may transmit the disease to her child if the X-chromosome transferred by her is the affected one. The cross can be shown as in the image.