title: Challenging the system.
mesh_terms: D000818:Animals; D015509:Developmental Biology / Q000379:methods*; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D049490:Systems Biology / Q000379:methods*