Question

What do you understand by sex-linked characters? A normal man marries either a colour blind or a carrier woman. Predict the kind of children which may be expected in both the conditions.

Answer 1

Case 1	X${}^c$	X${}^c$
X	XX${}^c$ (carrier daughter)	XX${}^c$ (carrier daughter)
Y	X${}^c$Y (colour blind son)	X${}^c$Y (colour blind son)

Case 2	X	X${}^c$
X	XX (normal daughter)	XX${}^c$ (carrier daughter)
Y	XY (normal son)	X${}^c$Y (colour blind son)

A character is an observable property of an organism that is under genetic control. If this character is determined by the presence of X or Y chromosome then it is called sex-linked character.

Colour blindness is an X-linked disease and the person is said to be colour blind if it has a defective X chromosome. A normal man means its genotype is XY (no defective X).

Case 1: Normal man (XY) marries the colour blind woman (X${}^c$X${}^c$)

100% daughters will be carrier while 100% son will be colour blind. This is because of the defective X chromosomes received from the mother.

Case 2: Normal man (XY) marries carrier woman (XX${}^c$)

50% daughters will be carrier and 50% normal while 50% son will be normal and 50% colour blind. This is because of only one defective X chromosome present in the mother.