Body plan development and Hox genes

In a nutshell

The development of body plans of many organisms are controlled by certain genes called Hox genes. This genes lead to the production of proteins that ensure the correct body parts develop in the correct place. Apoptosis and mitosis are also responsible for the formation of body plans.

Body plans

Definition

Body plans are general structures of an organism and the certain way that they are arranged.

Certain genes control the development of body plans, this is because proteins coded for by these genes are responsible for the basic body plan and ensuring the right body parts are in the right place. These genes are called Hox genes.

Hox genes

Hox genes are found in animals, fungi and plants. Hox genes have regions called homeobox sequences that have not changed much over time during the evolution of organisms. This is why homeobox sequences are described as being highly conserved.

The process by which Hox genes work is described below.

1.	Homeobox sequences encode for homeodomains which are parts of a protein.
2.	The homeodomain binds to specific DNA regions, this allows the protein to act as a transcription factor.
3.	This activates or represses transcription of developmental genes so directly affects proteins involved in the formation of a body plan.

Drosophila hox genes

In Drosophila (fruit flies), there are two Hox gene clusters. One is responsible for the development of the head and anterior thorax; the other is responsible for the development of the posterior thorax and abdomen.

Biology; Patterns of inheritance; KS5 Year 12; Body plan development and Hox genes — 1. Head, 2. Thorax, 3. Abdomen, 4. Chromosome, 5. Gene cluster one, 6. Gene cluster two.

Apoptosis and mitosis

Apoptosis and mitosis are both involved in body plan development. Apoptosis refers to the normal part of development where cells die and break down. It is sometimes called programmed cell death and is a highly controlled process that is described below.

1.	The cell dies by apoptosis.
2.	Components of the cells, such as protein and DNA, are broken down by enzymes.
3.	The cell begins to shrink and break into small fragments.
4.	Phagocytes engulf cell fragments and they are digested.

Mitosis and the differentiation of cells are processes that are heavily involved in the creation of body parts. Apoptosis then removes unwanted structures by killing unwanted cells. This process is controlled by genes that switch on or off in certain cells.

These genes can also be switched on or off in response to stimuli.

Examples

DNA damage can cause the cell cycle to be paused which could trigger apoptosis genes.
Stress such as a lack of nutrients can prevent the cell from undergoing mitosis.
Pathogen invasion can trigger apoptosis genes to be expressed.