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Principles Of Inheritance And Variation

Question
CBSEENBI12046942
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Assertion : Haemophilia is a recessive sex linked disease.

Reason : Haemophilia occurs due to mutation of a structural gene on chromosome 15.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false

Solution

C.

If assertion is true but reason is false

Haemophilia is also known as bleeder disease. It is an example of sex linked inheritance in humans. It is either of two hereditary disorders in which the blood clots very slowly, due to a deficiency of either of two coagulation factors -

  1. Haemophilia A- It is due to deficiency of factor VIII (antihaemophilic factor)
  2. Haemophilia B- It is due to deficiency of factor IX (Christmas factor).

The patient may experience prolonged bleeding following any injury or wound, and in severe cases there is spontaneous bleeding into muscles and joints. It is controlled by a sex-linked gene, which means that it is almost exclusively restricted to males; women can carry the disease- and pass it on to their sons- without being affected themselves. The genes encoding factors VIII and IX have been used in gene therapy trials for haemophilia.

Mutations of a structural gene on chromosome 15 is the molecular basis of Marfan syndrome. It is due to dominant mutation resulting in the production of abnormal form of connective tissues and characteritic extreme looseness of joints.

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