Explain how the inheritance pattern of sickle cell differ from haemophilia. Any three.

• Sickle cell anaemia

  • Autosomal recessive disease
  • Transmission − From parent to offspring when both parents are carriers of disease
  • Pair of alleles Hb ^A and Hb ^S controls the expression of this disease.
    Hb ^A and Hb ^A − Normal
    Hb ^A and Hb ^S − Carrier of disease
    Hb ^S and Hb ^S − Diseased
  • Cause of the disease − Change in gene causes the replacement of GAG by GUG leading to the substitution of Glu by Val at sixth position of beta globin chain of haemoglobin.
  • The mutant haemoglobin so formed polymerises at low oxygen tension, resulting in change in shape of RBC to sickle-like.

Hemophilia is an X linked genetic disorder in which the person suffering does not develop a proper blood clotting mechanism.Haemophilia is a congenital disease or genetically inherited disease. It is caused by the deficiency of Factor VIII, an important clotting factor.

The mutation in the genome leads to this deficiency. It occurs mainly in males.The gene for this factor is carried on the X-Chromosome. This gene appears in the normal (dominant) and the mutant (recessive form).

Females have X X chromosomes while males have only one X with Y chromosome, so for a female to get affected by haemophilia she has to have the mutant gene on both the X chromosomes while males may be affected if the carry it on the one X chromosome.

It has been observed that if only one X chromosome is carrying the mutant gene, that female does not have the disease, but she is a carrier.