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a. Why are colour blindness and thalassemia categorised as Mendelian disorders? Write the symptoms of these diseases seen in people suffering from them. b. About 8% of human male population suffers from colourblindness whereas only about 0.4% of human female population suffers from this disease. Write an explanation to show how it is possible. |
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Answer» a. Both are caused due to mutation or alteration in a single gene, and follow Mendelian inheritance, therefore, they are called Mendelian disorders. Symptoms of colour blindness: unable to discriminate between red and green colours. Symptoms of thalassemia: formation of abnormal haemoglobin resulting in Anaemia. b. ▪ Thalassemia a. It is an autosome-linked recessive disease. b. It occurs due to either mutation or deletion resulting in reduced rate of synthesis of one of globin chains of haemoglobin. c. Anaemia is the characteristic of this disease. d. Thalassemia is classified into two types: a. α-thalassemia—Production of α-globin chain is affected. It is controlled by the closely linked genes HbA1 and HbA2 on chromosome 16. It occurs due to mutation or deletion of one or more of the four genes. b. β-thalassemia—Production of β-globin chain is affected. It occurs due to mutation of one or both HbB genes on chromosome 11. ▪ Colour blindness a. It is a sex-linked recessive disorder. b. It results in defect in either red or/and green cone of eye, resulting in failure to discriminate between red and green colour. c. The gene for Colour blindness is present on X chromosome. d. It is observed more in males (XcY) because of presence of only one X chromosome as compared to two chromosomes of females. |
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