**Core Concept**
Cleft lip is a congenital anomaly resulting from the incomplete fusion of the medial nasal prominence and the maxillary prominence during embryonic development. This occurs between the 3rd to 7th week of gestation, leading to a physical deformity in the upper lip and primary palate.

**Why the Correct Answer is Right**
The correct answer is related to the embryological development of the face. Cleft lip is associated with the failure of the medial nasal prominence to fuse with the maxillary prominence. This fusion is crucial for the formation of the upper lip and primary palate. The palatine shelves, which develop from the maxillary prominences, also fail to fuse with the medial nasal prominence, resulting in a cleft lip and palate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as cleft lip is not primarily caused by genetic mutations, although some genetic syndromes may be associated with an increased risk.
**Option B:** This option is incorrect as cleft lip is not a result of environmental factors during pregnancy, although maternal smoking and certain medications may increase the risk.
**Option C:** This option is incorrect as cleft lip is not a result of poor nutrition during pregnancy, although some studies suggest a possible link between maternal nutrition and the risk of cleft lip.

**Clinical Pearl / High-Yield Fact**
Cleft lip and palate are the most common congenital anomalies of the face, affecting approximately 1 in 700 births. Early surgical repair is crucial to improve feeding, speech, and social outcomes.

**Correct Answer:**