Practice question

Specification and determination both indicate commitment but differ fundamentally in stability and reversibility. Specification is labile; tissue cultured neutrally follows preferred pathway, yet when grafted into foreign embryonic region receiving different BMP, Wnt or FGF signals, it can alter fate to match host. Determination involves molecular lockdown through cis-regulatory modifications, DNA methylation, Polycomb repression of alternative programs and autoregulatory transcription factor circuits exemplified by MyoD autoactivation in muscle. Determined cells maintain donor identity after transplantation into confrontational environments, resisting reprogramming and demonstrating self-sustaining fate maintenance without ongoing external instruction.