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

A character refers to a genetically controlled observable trait or property of an organism. When sex chromosomes are involved, the character becomes sex-linked.

Complete solution: If the presence of X or Y chromosome (sex-chromosomes) determine the expression of a character, then it is called a sex-linked character. An example of a sex-linked disease is colour blindness. It is an X-linked disease. A person would be colour blind if he/she has a defective X chromosome.
Considering, ${X^c}$ as the defective X chromosome responsible for colour blindness.
Then, the genotype of a normal man: XY (no defective X)
The genotype of a colour blind woman: ${X^c}{X^c}$
The genotype of a carrier woman: $X{X^c}$
Case I: A normal man (XY) marries a colour blind woman $\left( {{X^c}{X^c}} \right)$.

Gametes	Xc	Xc
X	XcXc(colour blind daughter)	XcXc(colour blind daughter)
Y	XcY(colour blind son)	XcY(colour blind son)

In this case, all the sons and daughters would get colour blindness.
The case I: A normal man (XY) marries a carrier woman (XXc).

Gametes	X	Xc
X	XX(normal daughter)	XXc(carrier daughter)
Y	XY(normal son)	XcY(colour blind son

In this case, $50\%$ daughters would be normal; others $50\%$ would be carriers. Among sons, $50\%$ would be normal and the rest would have colour-blindness.

Note: Colour blindness is a recessive X-linked disease. Presence of the gene in a single X chromosome of females makes them a carrier for the disease. As males have only one X chromosome and if it has the concerned gene then the male would be affected.