Question

Acatalasia is reduction or absence of catalase in the blood and tissues, leading to the appearance of ulcers on the gums and loss of teeth - the type of inheritance is autosomal recessive. The absence of lateral upper incisors is inherited as a recessive trait linked to the X-chromosome. In a family where the wife is healthy, and the husband has no incisors, a daughter was born, who at the age of ten appeared ulcers on the gums. A biochemical blood test showed a decrease in catalase. The younger son is missing incisors. Evaluate the probability of having children with both abnormalities in this family.

Answer 1

In autosomal recessive disease both the alleles should be recessive(aa) and in X linked recessive both X should be recessive in female (Xi Xi ) and one X recessive in males(Xi Y) .Since the mother is healthy but the daughter has acatalasia both the mother and father have to be carriers for the disease. Since the son has missing incisors the mother has to be a carrier for that disease as well. So genotype of the mother will be AaXXi and that of the father should be AaXiY. So the cross between them will be

	AX	aX	AXi	aXi
AXi	AAXXi	AaXXi	AAXi Xi	AaXi Xi
aXi	AaXXi	aaXXi	AaXi Xi	aaXi Xi
AY	AAXY	AaXY	AAXi Y	AaXi Y
aY	AaXY	aaXY	aAXi Y	aaXi Y

The highlighted genotypes indicate children with both the abnormalities.

So, probability of children with both abnormalities =2/16 =1/8