Experimental Observations and Their Interpretations

• The removal of the AER causes immediate cessation of limb development (statement A), demonstrating that the AER provides essential growth signals (such as FGF family members) that maintain proliferation in the underlying mesenchyme.

• Placing leg mesenchyme beneath the wing AER results in distal hindlimb structures forming at the forelimb tip (statement B), indicating the mesenchyme carries limb identity (wing vs. leg) intrinsically. The AER functions permissively to stimulate outgrowth but does not determine limb identity.

• In line with above, statement E that the AER does not specify limb type but sustains outgrowth is supported, reinforcing the notion that mesenchymal identity is dominant in determining limb fate.

• Statement C, that the AER specifies wing or leg identity, is contradicted by these experiments. The identity remains mesenchyme-driven even under AER influence.

• Statement D acknowledging the AER’s role in sustained outgrowth and development is also supported by experimental evidence.

Correct Combination of Statements Based on the Experiment

• Supported: A (limb mesenchyme induces/sustains AER), B (mesenchyme specifies limb type), D (AER responsible for growth), E (AER does not specify limb type)

• Unsupported: C (AER specifies limb type)

Thus, the valid combination is:
(2) A, B, D and E only

Conclusion

The chick wing development experiments collectively demonstrate that limb mesenchyme induces and sustains the AER, mesenchyme specifies limb identity (wing vs leg), and the AER governs sustained limb outgrowth but does not confer identity. This highlights critical reciprocal tissue interactions vital for proper limb morphogenesis.

Final answer:
(2) A, B, D and E only