How might hox genes contribute to variation?
Hox genes are a group of related genes that specify the anterior-posterior axis and segment identity of metazoan organisms during early embryonic development. These genes are critical for the proper number and placement of embryonic segment structures (such as legs, antennae, and eyes). Homeotic genes are defined by a DNA sequence known as the homeobox, which is a sequence of 180 nucleotides that code for a protein domain known as the homeodomain. The protein products of homeotic genes belong to a class of proteins known as transcription factors, all of which are capable of binding to DNA, thereby regulating the transcription of genes. Just as homeotic genes regulate realisator genes, they are in turn regulated themselves by gap genes and pair-rule genes, which are in their turn regulated by maternally-supplied mRNA. This results in a transcription factor cascade: maternal turns on gap or pair-rule genes; gap and pair-rule genes turn on homeotic genes; then, finally, homeotic genes tur
