After first cell divisions, genes {gap gene} {hunchback gene} {hunchback-maternal gene} {knirps gene} {Kruppel gene} can code zinc-finger transcription factors that make bands along embryo and body regions by working with maternal-effect genes and by repressing each other. Gap genes also regulate genes expressed later. Transcription-factor binding sites are high-affinity or low-affinity, so transcription-factor concentration affects which genes transcribe and how much, leading to gradients and bands. In small regions, same chemicals cause different effects.
After gap-gene expression, genes {segmentation gene} can code for transcription factors that segment body, pair segments, and make segment polarity. Segmentation genes work with gap-gene products, and interact with each other using autofeedback, to sharpen segment boundaries. Segmentation genes include pair-rule genes, such as fushi tarazu gene, even-skipped gene, hairy gene, runt gene, and eve gene.
Segmentation genes {pair-rule gene} {eve gene} {even-skipped gene} {fushi tarazu gene} {hairy gene} {runt gene} can be about splitting body regions. In small regions, same chemicals cause different effects.
Genes {segment polarity gene} can be about front and back. In small regions, same chemicals can cause different effects.
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Date Modified: 2022.0225