Sinh học - Chapter 32: Introduction to animal evolution

(5) The transformation of a zygote to an animal of specific form depends on the controlled expression in the developing embryo of special regulatory genes called Hox genes. These genes regulate the expression of other genes. Many of these Hox genes contain common “modules” of DNA sequences, called homeoboxes. Only animals possess genes that are both homeobox-containing in structure and homeotic in function. All animals, from sponges to the most complex insects and vertebrates have Hox genes, with the number of Hox genes correlated with complexity of the animal’s anatomy.