In contrast to Drosophila, some insects (e.g., centipedes) have legs on almost every segment posterior to the head. Based on your knowledge of Drosophila, propose a genetic explanation for this phenotype, and describe the expected expression patterns of genes of the Antennapedia and bithorax complexes.

Key Concepts

Homeotic Genes

Homeotic genes are crucial in determining the identity of body segments during development. In Drosophila, these genes, such as those in the Antennapedia and bithorax complexes, dictate the formation of specific structures in each segment. Mutations in these genes can lead to the transformation of one body part into another, illustrating their role in segment identity.

Antennapedia Complex

The Antennapedia complex is a group of homeotic genes in Drosophila that primarily regulates the development of the thoracic segments. When expressed, these genes promote the formation of legs in the appropriate segments. Misexpression or mutations can result in legs developing in place of antennae, highlighting the complex's role in segmental identity and limb formation.

Bithorax Complex

The bithorax complex consists of homeotic genes that control the development of the posterior segments in Drosophila, particularly the abdomen and the second thoracic segment. This complex is responsible for specifying the identity of these segments, and alterations in its expression can lead to transformations, such as the development of additional wings or altered segment structures, which can help explain variations in limb development across different insect species.