Practice question

Early Drosophila nuclear cycles are driven maternally with synchronous S-M phases and minimal transcription due to chromatin compaction and high mitotic rate. Minor wave of zygotic genome activation around nuclear cycle 11 sees transcription of few genes like early even-skipped stripe enhancers, fushi-tarazu and sex determination genes Sex-lethal. This precedes major activation at cycle 14 linked to cellularization and cell cycle lengthening mediated by nuclear-to-cytoplasmic ratio sensing via Chk1 checkpoint. Cycle 11 marks first detectable zygotic transcription detectable by in situ hybridization, representing onset before mid-blastula transition large-scale activation.