Question

Mention any two autosomal genetic disorders with their symptoms.

Answer 1

Hint: In autosomal recessive inheritance, the two or both the copies of the gene present in each cell have mutations. The parents of an individual offspring with an autosomal recessive condition contains one copy of the mutated gene, but they always do not show signs and symptoms of the condition.

Complete answer:
The two autosomal recessive traits are:-
(i) Sickle-cell anaemia : As it is an autosomal recessive disease therefore it can be transmitted from parents to the offspring when both male and female individuals are carriers (heterozygous) for the gene. The disease is controlled by a single pair of allele, HbA and HbS. Thus three genotypes are possible in population
HbA HbA (Normal, homozygous)
HbA HbS (Normal, carrier)
Hbs Hbs (Diseased, die before attaining maturity)
Heterozygous (HbA HBS) individuals appear apparently unaffected but they are carriers of the disease as there is 50% probability of transmission of the mutant gene to the progeny, thus exhibiting sickle-cell trait.
The disease/defect is caused by mutation (transversion) of the gene controlling B-chain of haemoglobin. The mutated gene is called HbS. Hb causes one change in amino acid sequence of B-chain. It replaces glutamic acid (Glu) present at 6th position of the B-chain by amino acid valine (Val). The mutant haemoglobin molecule undergoes polymerisation under low $\mathop O\nolimits_2 $ tension causing the change in the shape of the RBC from biconcave disc to elongated sickle-like structure.
(ii) Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks a liver enzyme called phenylalanine hydroxylase that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenyl pyruvic acid and other derivatives. Accumulation of these in the brain results in mental retardation These are also excreted through urine because of its poor absorption by the kidney.

Note: One more type of autosomal recessive disorder is :-
Thalassemia : Thalassemia is a recessive autosomal genetic defect, originated in Mediterranean region by their mutation or deletion recessive autosomal. Thalassemia are a group of disorders caused by defects in the synthesis of globin polypeptide in RBC. Absence or reduced synthesis of one of the globin chains results in an excess of the other.