Correct option is C
Explanation-
Option a : "As the limb grows outward, the stylopod forms first, then the zeugopod and the autopod is formed last. Each phase is characterized by a specific pattern of Hox gene expression - CORRECT
Stylopod (proximal; e.g., humerus) forms first, followed by zeugopod (e.g., radius/ulna), then autopod (distal; e.g., fingers). Hox genes indeed regulate positional identity along the limb axis.
Option b : "The zone of polarizing activity (ZPA) is maintained by the interaction of the FGFs from the AER and Shh expressed from the mesenchyme." - CORRECT
ZPA expresses Shh (Sonic hedgehog) and its maintenance involves interaction with FGFs from the apical ectodermal ridge (AER). FGF4 and FGF8 from AER help maintain Shh expression in ZPA (positive feedback loop). Shh also helps sustain FGF expression in AER (via Gremlin/BMP inhibition).
Option c : "Although cell death in the limb is necessary for the formation of digits and joints, it is never mediated by the BMPs, which is only responsible for differentiating mesenchyme cells into cartilage." - INCORRECT
BMPs (Bone Morphogenetic Proteins) do mediate apoptosis required for digit separation (removal of interdigital tissue). BMPs have dual roles is that they induce cell death in interdigital zones and also promote chondrogenesis (cartilage formation). In mouse or chick embryos, blocking BMP signaling results in webbed digits.
Option d : "The dorsal-ventral axis is formed in part by the expression of Wnt7a in the dorsal portion of the limb ectoderm, which maintains expression level of Shh in the ZPA and Fgf4 in the posterior AER." - CORRECT
Wnt7a specifies dorsal identity in the limb and contributes to the expression of Shh and Fgf4 indirectly via signaling networks.
Final Answer: Option c is not correct regarding tetrapod limb development that makes it a correct answer.
