Body Plans

• A body plan is the general structure of an organism that are arranged in a specific way.
• Proteins control the development of a body plan - they help set up the body plan so that everything is in the right place
• The proteins that control body plan development are coded for by genes called Hox genes.
• Similar Hox genes are found in animals, plants and fungi, which means that body plan development is controlled in a similar way.
• Hox genes have regions called homeobox sequences which are highly conserved - this means that these sequences have changed very little during the evolution of different organisms.
• Homeobox sequences code for a part of the protein called the homeodomain.
• The homeodomain binds to specific sites on DNA, enabling the protein to work as a transcription factor.
• The proteins bind to DNA at the start of developmental gens, activating or repressing transcription and so altering the production of proteins involved in the development of the body plan.
• Some cells die and break down as a normal part of development. This is a highly controlled process called apoptosis, or programmed cell death.
• Once apoptosis has been triggered the cell is broken down in a series of steps:

  • Enzymes inside the cell break down important components
  • Cell shrinks and breaks up into fragments
  • Fragments are engulfed by phagocytes and digested.