(a) Thalassemia and Haemophilia are categorised as Mendelian disorders because they occur by mutation in a single gene and their mode of inheritance follows the principles of Mendelian genetics. [1]
Symptoms of Thalassaemia
Symptoms of Haemophilia
A haemophilic patient suffers from non-stop bleeding even on a simple cut, which may lead to death. [0.5]
Pattern of Inheritance of Thalassaemia [1]
It is an autosome -linked recessive blood disease
Pair of alleles
HbA and
HbT controls the expression of this disease.
Conditions for thalassaemia :
HbA and
HbA : Normal
HbA and
HbT : Carrier
HbT and
HbT : Diseased
Let us assume that both father and mother are the carriers
(HbAHbT) of beta thalassaemia.
Parents:
HbAHbT HbAHbT (Father)
× (Mother)
Offspring:
HbAHbA HbAHbT HbAHbT HbTHbT NormalCarrier childCarrier childChild withwithwithseverethalassaemiathalassaemiathalassaemiatraittrait Pattern of Inheritance of Haemophilia : [1]
Haemophilia is an X-linked recessive genetic disorder.
Conditions for haemophilia :
XY;XX : Normal
XhY : Haemophilic male
XhX : Carrier female
XhXh : Haemophilic female
Let us assume that a carrier female
(XhX) is married to a normal male.
![](https://search-static.byjusweb.com/question-images/byjus/infinitestudent-images/ckeditor_assets/pictures/547759/original_52.png)
(b) When a normal male marries a carrier female (she is considered normal as she contains the mutant gene on one of her X chromosomes), they can produce a haemophilic son. So, the genotype of the parents would be XY and
XhX. [1]