Question

(a) Why are thalassemia and haemophilia categorized as Mendelian disorders ? Write the symptoms of these diseases. Explain their pattern of inheritance in humans.
(b) Write the genotypes of the normal parents producing a haemophilic son.

Answer 1

Explanation:

Mendelian disorders are the disorders which include genetic disorders that are caused by mutations or alterations in a single gene. Haemophilia and thalassemia are the disorders which are categorized under Mendelian disorders.

(a) Haemophilia: It is an X- linked recessive disorder which is more common in males than in females. Haemophilia is caused because of the defect in one of the blood clotting factors.

Haemophilia in males is inherited from heterozygous mother who is a carrier and these males shows infertility. In females both the X Chromosomes have to be in recessive form and thus they are rarely haemophilic.

The symptoms of this disease is that if there is an injury then there is a spontaneous bleeding which becomes difficult to be stopped.

b) Thalassemia: Thalaessemia is an autosomal recessive disorder of blood.

In thalassemia an abnormal haemoglobin is produced which decreases the blood's oxygen carrying capacity. Anaemia is caused due to the destruction of blood cells.

The symptoms of Thalassemia includes weakness, fatigue, slow growth, Dark urine etc.

If in an individual one of the parent is a carrier , then it also become carrier for the disease.

The individual has 25% chance of inheriting the Thalassemia disease, if both the parents are carriers for the disease.

(b) The genotype of the normal parents which are having a haemophilic son are as follows:

Parents :          XY     X     $X^h$X

                    (Father)       (Mother)

Offspring :     $X^h$X                      XX                          $X^h$Y                   XY

  (Carrier Daughter)   (Normal Daughter) (Haemophilic Son) (Normal son)