Question

Base substitution caused by base analogues is

• A. Transition
• B. Transversion
• C. Complementation
• D. None of the above

Answer 1

Answer: (A)

Transition

Exchange of one nitrogenous base for another base is called as substitution. Transition is the substitution of one type of base by other of its own type. Hence, purine is replaced with purine (adenine to guanine and vice versa) and pyrimidine is replaced with the pyrimidine (cytosine to thymine/uracil and vice versa) only.

Substitution of purine base for a pyrimidine base or substitution of pyrimidine base for a purine base is called as transversion. Hence, adenine is replaced with thymine/uracil and guanine with cytosine.

The complementation test is done to determine if two recessive mutations, that have to arise independently but produce the same phenotype, are alleles.

So, the correct answer is option A.