Five Mark Questions :
(a) Why are thalassemia and haemophilia categorized as Mendelian disorders? Write the symptoms of these diseases.Explain their pattern of inheritance in humans?
(b) Write genotypes of normal parents producing a haemophilic son.

A) Haemophilia is a sex-linked disorder. In haemophilia, the blood fails to clot when exposed to air and even a small skin injury results in continuous bleeding and can lead to death from the loss of blood. The recessive X linked gene for haemophilia shows characteristic criss-cross inheritance. It's a single gene in male results and disease haemophilia, where is a woman needs two such genes for the same.

Thalassemia is human anaemia due to an autosomal mutant gene and when the screen is present in homozygous condition this is a severe thalassemia major which is lethal. A heterozygous person shows a mild disease. The person suffering from thalassemia major is unable to produce adult chain. Haemoglobin contains delta change like that of the fetus which is unable to carry out normal oxygen transport function.

B) When normal parents produce a hemophilic son it means that the female must be a carrier of the gen so, the genotype of the son will be XʰY.