Body plans are the basic structural designs of different organisms, determined by genetic and developmental factors.

Homeobox genes are a group of regulatory genes with a conserved DNA sequence (homeobox sequence) that guides development of body plans.

Homeobox genes code for homeodomains on proteins.

A homeodomain is a part of the protein that binds to DNA. This allows them to switch genes on or off, affecting transcription and controlling the development of body plans.

Hox genes are a subset of homeobox genes in animals, crucial for correct positioning of body parts.

Humans have 39 Hox genes, which are likely derived from a single ancestral homeobox gene.

1. Control the number of body layers
2. Control symmetry of the body
3. Control the anterior-posterior axis, ensuring a head is at one end and a tail (if present) is at the other
4. Control position and development of limbs
5. Control segmentation of the body into head, thorax, abdomen, and so on
6. Control position and development of eyes and other important structures

1. Fewer ethical concerns than other animals
2. Low cost
3. Their genetics and development are well understood
4. Rapid reproduction rate
5. Simple body plan
6. Their mutations can be studied with a low-powered microscope

Regulatory genes, such as those that regulate the cell cycle and apoptosis, are able to respond to internal stimuli like stress, drugs, or hormones.

They can also respond to external stimuli like changes in temperature or light intensity.

Apoptosis removes unwanted cells, and can stimulate tissue remodelling.

For instance, apoptosis is responsible for removing the webbing between toes during human embryo development.

Homeobox genes very important and a mutation would have large effects by altering the organism's body plan.

Many other genes would also be affected by a mutation in a homeobox gene, so mutations are likely to be lethal and selected against.

Hox genes control the rate and location of cell division during growth and tissue formation, and they also control programmed cell death during development.