Practice question

Segmentation hierarchy subdivides embryo starting with maternal gradients regulating gap genes expressed in broad domains covering multiple adjacent segment primordia. Their proteins regulate pair-rule genes. Gap mutations delete large continuous regions, cuticle shows gap of denticle belts encompassing several segments leaving embryo shorter. Pair-rule mutations remove every other segment, segment polarity causes polarity reversals, homeotic transforms identity without loss. Therefore large deletions hallmark gap class named after conspicuous holes in larval cuticle, reflecting role integrating maternal information into regional subdivisions before periodic patterning emerges in blastoderm stage during early development.