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Q.
Transition mutation is due to replacement of
Molecular Basis of Inheritance
Solution:
Substitution (Replacement): In substitution a nitrogen base is changed with another base. It is of two types—transition and tranversion 1. Transition : Purine is replaced by purine $\left(A\ce{<=>}G\right)$ while pyrimidine is replaced by pyrimidine $\left(C\ce{<=>}T,C\ce{<=>} U\right)$, 2. Transversion : Purine is replaced by pyrimidine $\left(A \to C\right)$ while pyrimidine is replaced by purine $\left(C \to A\right), e.g.: SCA \left(GAG \to GUG\right).$ A classical example of point mutation is a change of single base pair in the gene for beta globin chain that results in the change of amino acid residue glutamate to valine. It results into a diseased condition called as sickle cell anemia.