Thalassemia and haemophilia are categorised as Mendelien disorders because they occur by mutation in a single gene. Their mode of inheritance follows the principles of Mendelian genetics. Mendelian disorders can be :
(i) Autosomal dominant (muscular dystrophy)
(ii) Autosomal recessive (thalassemia)
(iii) Sex linked (haemophilia)
Symptoms of thalassemia :
Thalassemia minor results only in mild anaemia, characterised by low, haemoglobin level.
Thalassemia major is also known as Cooley's anaemia. In this disease, affected infants are normal but as they reach 6 to 9 months of age, they develop severe altaemia, skeletal deformities, jaundice, fatigue etc.
Symptoms of Haemophilia : Persons suffering from this disease does not develop a proper blood clotting mechanism. A haemophilic patient suffers from non-stop bleeding even on a simple cut, which may lead to death.
Patterns of inheritance of Thalassemia :
Pairs of alleles HbA and HbT controls the expression of this disease.
Patterns of inheritance of Haemophilia :
It is X-linked genetic disorder. Compared to females, males have higher chances of getting affected because females have XX chromosomes while males have only one X with Y chromosomes. Thus, for a female to get affected by haemophilia, she has to have the mutant gene on both the X-chromosomes while males can be affected if they carry it on the single X-chromosome.
Conditions for haemophilia :
XX, XX - Normal
XhY - Haemophilic
XhX - Carrier
XhXh-Haemophilic
Let us assume that a carrier female (XhX) is married to a normal male :
