Homeotic gene

[2] Mutations in homeotic genes cause displaced body parts (homeosis), such as antennae growing at the posterior of the fly instead of at the head.

The antennapedia complex consists of five genes, including proboscipedia, and is involved in the development of the front of the embryo, forming the segments of the head and thorax.

[11] The bithorax complex consists of three main genes and is involved in the development of the back of the embryo, namely the abdomen and the posterior segments of the thorax.

[12] During development (starting at the blastoderm stage of the embryo), these genes are constantly expressed to assign structures and roles to the different segments of the fly's body.

For example, in one study, a pathogenic phytoplasma caused homeotic genes in a flowering plant to either be significantly upregulated or downregulated.

This led to severe phenotypic changes including dwarfing, defects in the pistils, hypopigmentation, and the development of leaf-like structures on most floral organs.