Explain the causes, inheritance pattern and symptoms of any two Mendelian genetic disorders.

Explanation

Haemophilia
Causes - In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected.
Inheritance pattern This is a sex linked recessive disease which shows its transmission from unaffected carrier female to some of the male progeny It shows criss cross inheritance. The heterozygous female carrier) for haemophilia may transmit the disease to sons. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and father should be haemophilic
Symptoms - In affected individuals, a simple cut will result in non-stop bleeding Sickle-cell anaemia
Causes - This defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule due to substitution of codon GAG to GUG
Inheritance pattern - This is an autosome linked recessive trait that can be transmitted from parents to offspring when both the partners are carrier for the gene (or heterozygous). This disease is controlled by a single pair of allele Hb and Hb. Out of the three possible genotypes Hb Hb. Hb Hb and Hb Hb only the last one shows the diseased phenotype. Heterozygous Hb Hb'] individuals appear apparently unaffected but they are carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny, thus exhibiting sickle - cell trait.
Symptoms - Under low oxygen tension the shape of the RBC changes to elongated sickle like structure from usual biconcave disc due to polymerisation of haemoglobin, resulting in decreased oxygen carrying capacity of blood.