Question

(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 colour blindness whereas only about 0.4% of human female population suffers from this disease. Write an explanation to show how it is possible.

Answer 1

a) Thalassemia:

Thalassemia is an inherited autosomal recessive disorder which affects the blood. Haemoglobin synthesized by the body is abnormal and is unable to carry oxygen efficiently. This later leads to the destruction of blood cells and thereby causes anemia. The individuals whose one of the parents is a carrier also becomes a carrier of the disease. If both the parents are carriers of the disease, the individual has 25% chance of inheriting the disease. Thalassemia is a life seizing disorder which does not allow the individual to live more than early stages of life. Different types of thalassemia exhibit different symptoms and severity. They include fatigue, weakness, pale appearance, yellow discoloration of skin (jaundice), facial bone deformities, slow growth, abdominal swelling, dark urine etc.

Colour blindness:

It is a genetic disorder which is inherited from the mother. Most of the colour blind people have red or green colour blindness. These people will not be able to see the colours which are mixed up or have little of red and green in them. The effects of colour blindness can be mild, moderate or severe.

(b) It is for sure that the male child inherits this colour blindness from the affected mother, as he obtains X chromosome from the mother which carries the gene for colour blindness. Hence, the majority of the male will be affected. Also, for the female to get affected, both the X needs to be defective i.e., affected or carrier mother and affected father. However, in male, only one X is present which needs to be affected. So, chances of suffering from this disease are more in males.