Question

If a colour blind man is married to a normal visioned woman whose parents are also normal visioned . What proportion of their children is likely to be colour blind?

Answer 1

Key: X Chromosome for normal allele and X” for recessive allele for colour blindness.

Homozygous normal female (XX) and a colorblind male X” Y

	X”	Y
X	XX” Carrier female	XY Normal Male
X	XX” Carrier female	XY Normal male

• The resulting Punnett Square, all of the females will inherit a normal X from their mother and a colorblind X” from their father, and thus will be heterozygous carriers of the trait and have normal vision.
• Since the sons inherit a normal X from their mother, and a Y from their father, they will also all have normal vision.
• There will not be a colour blind child in this generation.