Practice question

Gap genes encode transcription factors expressed in non-periodic domains defining large embryonic territories. Loss removes adjacent segment anlage covered by domain, resulting larvae missing head-thorax for hunchback, thoracic segments for Kruppel, abdominal segments for knirps or giant, producing large gaps. Phenotype contrasts with pair-rule where every other segment missing repeats, and segment polarity where polarity reversed. Duplications characterize wingless defects. Large region deletion remains diagnostic of gap function as intermediaries interpreting maternal morphogen concentrations into broad fields that later regulate periodic gene expression and establish positional values for subsequent metameric patterning during development.