**Core Concept**
Zidovudine, a nucleoside reverse transcriptase inhibitor (NRTI), is used in the treatment of HIV infection. Resistance to zidovudine occurs due to mutations in the reverse transcriptase gene of HIV, leading to altered enzyme activity and decreased drug efficacy.

**Why the Correct Answer is Right**
The most common mutation associated with zidovudine resistance is the M41L substitution, which results in a decreased affinity of the enzyme for the drug. This substitution occurs in the thumb subdomain of the reverse transcriptase enzyme, where zidovudine binds. As a result, the enzyme is less efficient at incorporating the nucleoside analog into the viral DNA, leading to reduced drug efficacy. Other mutations, such as D67N, T215Y, and K219Q, can also confer resistance to zidovudine.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to zidovudine resistance. The correct answer is related to specific mutations in the reverse transcriptase gene.
* **Option B:** This option is incorrect because it does not specify the correct mechanism of resistance. While mutations in the reverse transcriptase gene are indeed the cause of resistance, this option is too vague.
* **Option C:** This option is incorrect because it does not mention the specific mutations associated with zidovudine resistance.

**Clinical Pearl / High-Yield Fact**
It's essential to monitor for mutations in the reverse transcriptase gene, particularly the M41L substitution, when patients on zidovudine therapy exhibit decreased viral load suppression or increased viral loads.

**Correct Answer: C. Mutations in the reverse transcriptase gene, such as M41L, D67N, T215Y, and K219Q.**