Thalassemia and haemophilia categorised as Mendelian disorders.

Explanation

Thalassemia and haemophilia are categorised as Mendelian disorders because these disorders are due to alteration in a single gene. Also they are transmitted to offsprings through Mendelian principles of inheritance.
= Symptoms and pattern of inheritance are given below:
= (a) Thalassemia : It is an autosomal linked recessive blood disorder characterised by defects in `alpha , beta or delta `chain resulting in abnormal Hb molecule.
= Symptom : Anaemia
= Inheritance : Two mutant alleles (one from each parent) must be inherited for an individual to be affected i.e. homozygous. Heterozygous are carriers and may pass the mutant allele to children.
= (b) Haemophilia : It is a sex linked recessive disorder whose gene is located on X-chromosome.
= Symptom : Prolonged clotting time and external bleeding even in minor injury.
= Inheritance : The gene is present on X-chromosome, so it is inherited by males as they have single X-chromosome. Affected males are said to be hemizygous. Females have two X-chromosomes, thus possibility of them being affected is rare as the mother of such female has to be atleast carrier and father should be haemophilic.