Haemophilia is a sex-linked recessive disease. Study the pedigree analysis given below showing the inheritance

Question

Answer the following questions: 

A. Haemophilia is a sex-linked recessive disease. Study the pedigree analysis given below showing the inheritance of the disease in a family and answer the questions that follow.

i. Give the evidence from the above analysis which suggests that the disease is 

1. sex-linked and 

2. caused by a recessive allele. 

ii. Write the possible genotypes of the individuals ‘2’ and ‘5’.

B. Why is thalassemia categorised as a Mendelian disorder? State the condition when an individual will suffer from the disease.

Answer 1

A.

i. 

1. In all the generations, only the males are affected with the disease. 

2. The parents of the affected individuals are not affected which implies that they are carriers and the gene is recessive. 

ii. Possible genotype of ‘2’: Xd X Possible genotype of ‘5’: Xd Y

B. Thalassemia is categorised as Mendelian disorder because these are caused due to alteration or mutation in single gene and follow the Mendel’s principles of inheritance. It occurs due to either mutation or deletion resulting in reduced rate of synthesis of one of globin chains of haemoglobin.