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Hox Genes

“General purpose” control genes are important elements in building complicated organisms like flies. Some “control” genes are common to many organisms (they are homologous—inherited from our common ancestor). For example, Hox genes help lay out the basic body forms of many animals, including humans, flies, and worms. They set up the head-to-tail organization. You can think of them as directing instructions as an embryo develops: “Put the head here! Legs go over there!”

Hox genes lay out general body forms
They are general purpose in the sense that they are similar in many organisms; it doesn’t matter if it’s a mouse’s head or a fly’s head that is being built, the same gene directs the process. Small changes in such powerful regulatory genes, or changes in the genes turned on by them, could represent a major source of evolutionary change.  
 
Explore further
•  Types of developmental change
•  Ontogeny and phylogeny
•  Developmental constraints
•  Understanding complexity


• Mouse image courtesy of the National Institutes of Health.
• Fly head image courtesy of Wai Pang Chan, University of California, Berkeley.

Next Topic:
Genetic Drift


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Spanish translation of Understanding Evolution For Teachers from the Spanish Society of Evolutionary Biology.