Question

Consider the following and choose the correct answer Assertion [A]: Tautomeric shifts in DNA bases are a source of spontaneous mutations. Reason [R]: Rare tautomeric forms have altered hydrogen-bonding patterns. The correct answer is

• A. Both [A] and [R] are true and [R] is the correct explanation of [A]
• B. Both [A] and [R] are true and [R] is not the correct explanation of [A]
• C. [A] is true, but [R] is false
• D. [A] is false, but [R] is true

Hint:

Tautomeric shifts cause \[ \boxed{ \text{abnormal base pairing} } \] which leads to spontaneous point mutations during DNA replication.

Answer 1

The Correct Option is A

Step 1: Examine the assertion. Rare tautomeric forms of DNA bases can pair with incorrect complementary bases during DNA replication. This leads to spontaneous mutations. Hence, \[ \boxed{\text{Assertion [A] is true}.} \]

Step 2: Examine the reason. Tautomeric shifts alter the hydrogen-bonding pattern of nitrogenous bases. This causes abnormal base pairing, such as \[ A^*\!-\!C \quad\text{or}\quad G^*\!-\!T. \] Hence, \[ \boxed{\text{Reason [R] is true}.} \]

Step 3: Establish the relationship. The altered hydrogen-bonding pattern directly explains how tautomeric shifts produce spontaneous mutations. Therefore, \[ \boxed{ \text{Both [A] and [R] are true and [R] correctly explains [A].} } \] Thus, \[ \boxed{(A)} \] is the correct answer.