question_answer 20)

  In sickle-cell anaemia glutamic acid is replaced by valine. Which one of the following triplet codes for valine? (a) G G G                            (b) A A G                              (c) G A A                              (d) G U G

Answer:

                  (d) Sickle-cell anaemia is an autosome linked recessive trait. This disease is controlled by a single pair of allele  and  only the homozygous individuals for, i.e., shows the diseased phenotype. The heterozygous individuals are carriers (). Due to point mutation, glutamic acid (Glu) is replaced by valine (Val) at sixth position of (3-chain of haemoglobin molecule. This substitution occurs due to the single base substitution of the beta globin gene from GAG (Glu) to GUG (Val).Whereas, the other codes GGG, AAG. GAA do not codes for valine.