| Consider the following statements. |
| 1. Haemophilia is a sex-linked recessive disease. |
| 2. Down's syndrome is due to aneuploidy. |
| 3. Phenylketonuria is an autosomal recessive gene disorder. |
| 4. Phenylketonuria is an autosomal dominant gene disorder. |
| 5. Sickle cell anaemia is an X-linked recessive gene disorder. |
| Which of the statements given above are correct? |
A) 1, 3 and 5
B) 1 and 3
C) 2 and 5
D) 1, 2, 3 and 5
Correct Answer: D
Solution :
[d] Haemophilia or Bleeder's disease is a sex-linked (X-linked recessive) disease. It is a rare human blood disorder, in which blood clotting is deficient, resulting in severe bleeding internally and externally. The condition is due to lack of fibrin in the blood and is controlled by two closely linked genes on the X-chromosome that are responsible for the production of different clotting factors. Down's syndrome is caused due to trisomy of chromosome 21 (i.e. hyperploidy type of aneuploidy). It is a genetic condition in which a person has 47 chromosomes instead of the usual 46. Phenylketonuria is an autosomal recessive gene disorder. It is caused by the absence or deficiency of the enzyme phenylalanine hydroxylase which results in the accumulation of phenylalanine in all body fluids. Sickle cell anaemia in humans, is also inherited as an autosomal recessive disorder. It is caused by a change in a single base pair of DNA. It is a genetic disease reported from Negroes. In sickle cell anaemia haemoglobin the glutamic acid in p chain is replaced by valine. The individuals of sickle cell anaemia are immune to malaria.
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