Final answer:
The statement that most transcription factors active in early development are morphogens is false. Not all transcription factors are morphogens, even though both play essential roles in animal development. Hox genes demonstrate the conservation of these developmental mechanisms, suggesting a shared ancestry among diverse species.
Step-by-step explanation:
The statement most transcription factors that are active in early development are morphogens is false.
Morphogens are signaling molecules that diffuse through an embryonic space and cause different effects depending on their concentration. They help to pattern tissues in a concentration-dependent manner, such as in establishing the head to tail axis (anteroposterior polarization) in developing embryos. Although they are crucial in development, not all transcription factors are morphogens. Transcription factors are proteins that help turn genes on or off by binding to nearby DNA. While some morphogens can be transcription factors, not all transcription factors are morphogens.
Regarding the Hox genes, they provide a critical example of conserved molecular mechanisms across species, underscoring the concept of shared ancestry. Hox genes are a set of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. They express transcription factors that initiate and terminate the expression of specialized cells and tissues. Conservation of these genes and their associated transcription factors in a wide variety of animals suggests they are ancient aspects of the animal developmental program and that changes in these genes are subtle due to their critical roles.
Mutated promoters can affect transcription by altering the binding sites for transcription factors. For example, a mutation in the promoter can create a new binding site or abolish an existing one, thus increasing or decreasing the rate of transcription (mutated promoters).
In the context of early embryonic development, changes to critical genes are relatively minor, because early embryos are highly sensitive, and significant mutations can result in non-viability of the embryo. Also, there has not been much evolutionary time since the divergence of different animal taxa, meaning that the genes involved in early development are highly conserved.