The products of HOX genes are HOX proteins, which are transcription factors. These proteins bind to enhancer sections of DNA to repress or activate a specific set of genes. In Drosophila, HOX genes regulate the development of antennae and other appendages. During its embryonic development, there is the gradient of proteins determining, which end will be anterior and posterior, and which side will be dorsal and ventral. In conjunction with these proteins, HOX proteins activate or repress key genes, which result in the correct development of the appendages in the relevant body segment.
The animal’s body develops from one cell, and each new generation of cells carries the same initial set of chromosomes and genes minus germ cells, which do not appear immediately. A slightly different set of genes is activated in different tissues and parts of the body – and the cells develop according to a different scenario. Some form the legs of Drosophila; others form its antennas; others form wings, obeying the genes that conduct their growth and segment boundary separation. A malfunction of the genes is fraught for the fly with serious violations, for example, the appearance of an additional pair of wings or legs that have grown between the eyes in place of the antennas.