Why are thalassemia and haemophilia categorised as mendelian disorders .Write symptoms of these disease explain their pattern of inheritance in humans?
Answers
Answer:
Mendelian disorders include genetic disorders caused by alterations or mutations in a single gene as in haemophilia and thalassemia.
a) Haemophilia: It is a type of genetic disorder in which blood clotting ability of the body is impaired due to the defect in one of the blood clotting factors. It is an X- linked recessive disorder and therefore is more common in males than in females. Males can inherit this disease from heterozygous carrier mother and such males become infertile. Females are rarely haemophilic as both the X- chromosomes need to be in recessive form. This disease leads to spontaneous bleeding on injury.
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 defect in a, (3 or 8 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 internal bleeding, even in a minor injury.
Inheritance The gene is present on X-chromosome, so it is inherited by males as they have a single X-chromosome. Affected males are said to be hemizygous.