Given below is the representation of a relevant part of amino acid composition of the β-chain of haemoglobin, related to the shape of human red blood cells.

(a) Is this representation of the sequence of amino acids indicating a normal human or a sufferer from a certain blood related genetic

disease? Give reason in support of your answer.

(b) Why is the disease referred to as a Mendelian disorder? Explain.

OR

Name the kind of diseases/disorders and any two symptoms that are likely to occur in humans if:

(a) Mutation in the gene that codes for an enzyme phenylalanine

hydroxylase occurs.

(b) The karyotype is XXY.

a) The given sequence of amino acid composition indicates the relevant portion of the β-chain of haemoglobin of a normal human. Since the disease is caused by the substitution of Glutamic acid (GAG) by Valine (GUG) at the sixth position of the beta-globin chain of the haemoglobin molecule.

b) Mendelian disorders are transmitted to the offspring by following the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced to a family by the pedigree analysis and they are determined by

alteration or mutation in the single gene.

Note:

OR

• Phenylketonuria is an inborn error of metabolism is also inherited asthe autosomal recessive trait. In this disease the mutation in the gene that codes for an enzyme phenylalanine hydroxylase occur and the karyotype is XXY.

• Due to these the phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives.

• Accumulation of these substances in the brain results in mentalretardation.

• These are also excreted through urine because of its poor absorption by the kidney.