| Haemophilia or Bleeder’s disease | Defect in the blood which prevent clotting Haemophiliac bleeds excessively when injured sometime may leads to death. | It is a sex linked disease caused by recessive gene present on X chromosomes | Since the male have only one X chromosome and do not have its homologue so show the disease however the women are carrier because of one normal X chromosome & One with the defect they only pass the gene to next generation .The female with both the defective genes do not born because it is lethal. | Queen Victoria of England 1819—1901 was a carrier and her son had this defect who passed the genes to his daughter who became the carrier, this disease spread in the royal families of Spain and Russia through the marriage of two of Victoria’s daughters. |
| Sickle cell Anaemia | Change in the shape of RBC due to defective haemoglobin S or sickle cell haemoglobin. The individual with sickle shaped RBC have low oxygen carrying capacity | Abnormal haemoglobin ᵦ chain where on 6th position amino acd valine is present in place of amini acid glutamic acid. | Only heterozygotic individual are carrier and homozygous show the disease it is an autosomal hereditary disease .Affected individual produces when marriage between two heterozygous individuals takes place. | Tropical African have heterozygous condition that is a selective advantage because it lower the chances of developing malaria.Because malaria parasite do not survive on sickle shaped RBC. |
