1.

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

Answer» Haemophilia
(i) It is a sex-linked recessive disorder.
(ii) Patient continues to bleed even on a minor cut as the patient does not possess natural phenomenon of blood clotting.
(iii) The gene for haemophilia is located on X- chromosome.
(iv) So, more males suffer from haemophilia than females because in males single gene for the defect is able to express
(v) The defective alleles produce non-functional cascade of protein involved in blood clotting
(vi) Females suffer from this disease only in homozygous condition, i.e.,` X^(C)X^(C)`.
Sickle-cell Anaemia
(i) It is an autosomal linked recessive trait
(ii) The disease is controlled by a single pair of allele `H_(b)^(A) and H_(b)^(S)`
(iii) Only the homozygous individuals for `H_(b)^(S)`,ie., `H_(b)^(S)H_(b)^(S)` show the diseased phenotype.
(iv) The heterozygous individual are carriers `(H_(b)^(A)H_(b)^(S))`
(v) Due to point mutation Glutamic acid (Glu) is replaced by Valine (Val) at sixth positions of beta globin chain of haemoglobin molecule.
(vi) `H_(b)^(S)` behaves as normal haemoglobin except under oxygen stress where erythrocytes lose their circular shape and become sickle-shaped. As a result, the cells cannot pass through narrow capillaries are clogged and thus, affect blood supply to different organs.


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