(2) Mice of set A (with mutation in N-cadherin) will die in early development, but mice of set B (with mutation in N-CAM) will develop normally and show mild abnormalities in the development of the nervous system.

Explanation:

N-cadherin is a key calcium-dependent cell adhesion molecule critical for early embryonic development, especially in forming coherent epithelial sheets such as neuroepithelium. Research shows that disruption or mutation of N-cadherin results in severe developmental defects often lethal at early stages due to loss of proper cell-cell adhesion necessary for tissue morphogenesis and neural tube formation.

On the other hand, N-CAM (neural cell adhesion molecule), belonging to the immunoglobulin superfamily, modulates finer aspects of cell adhesion, particularly in neural tissue. Mutations or loss of N-CAM generally result in mild neurological abnormalities rather than early lethality, as its role is more related to fine tuning cell interactions, neural patterning, and synaptic functions.

Multiple in vivo studies and antibody blocking experiments indicate that N-cadherin loss severely disrupts neuroepithelial integrity and embryonic morphogenesis, while N-CAM mutants survive but exhibit subtle defects in the nervous system development such as altered cell migration or synaptic connectivity.