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

Explanation

Two Mendelian genetic disorders are as follows:
(i) Sickle-cell anaemia It is a blood related autosomal Mendelian genetic disorder. It occurs by a change of a single base pair in the gene, leading to substitution of glutamic acid by valine at the 6th position of B-globin since, its transmission follows Mendelian principles, it is called Mendelian disorder. Inheritance pattern It is transmitted from parents to the offspring, when both the partners are carriers (heterozygous) of the disease. In this disease, RBCs become sickle-shaped carrying less oxygen.
(ii) Phenylketonuria It occurs due to defective allele on the autosome. Its inheritance pattern is from parent, who are heterozygous for the gene to the offspring. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result, phenylalanine gets, accumulated and converted into phenyl pyruvate and other derivatives.
Symptoms Accumulation of these compounds in the brain causes mental retardation. They are also excreted in the urine.