Gene cascades: In birds and mammals, many genes control the development of genes. AS one gene is turned on, it releases transcription factor which in turn switch on another gene. That is, the products of many genes control the expression of others. This occues in a cascade of signals.
Homeotic Genes: Are important transcription factor genes which control the development of most organ systems.
Homologue/homeotic genes are similar DNA sequences found in different organisms. These include homeobox genes which have been found in a wide range of organisms. Since similar homeobox genes have been found in every eukaryote studied from fruit flies to humans, and the fact that they retain similar functioning in these organisms has lead scientists to the conclusion that they are further evidence of evolutionary relationships between organisms.
For cascades :
•Pattern formation (development of parts of body) is not controlled by a single gene - many genes need to be switched on or off in the appropriate sequence to form the various structures of the body e.g. limbs
•A gene cascade occurs as the action of each gene causes the next gene(s) to be turned on, like in limb development.
•As each gene is turned on, substances that turn on the next gene(s) are produced, called transcription factors. The expression of 1 gene can turn on multiple genes through the production of >1 protein.
•Vertebrate limbs begin as undifferentiated limb buds that give rise to their unique forms.
•Certain molecules induce the formation of a zone that secretes the sonic hedgehog factor, inducing nearby cells to form posterior structures such as limbs.
Hrm, I just realised how old this thread is, and how useless my reply is lol