A number of genes that control expression of Hox genes in Drosophila have been identified. One of these homozygous mutants is extra sex combs, where some of the head and all of the thorax and abdominal segments develop as the last abdominal segment. In other words, all affected segments develop as posterior segments. What does this phenotype tell you about which set of Hox genes is controlled by the extra sex combs gene?

Key Concepts

Hox Genes

Hox genes are a group of related genes that determine the body plan and segment identity during embryonic development in animals. They encode transcription factors that regulate the expression of other genes, influencing the formation of structures along the anterior-posterior axis. In Drosophila, specific Hox genes are responsible for segment identity, and mutations can lead to transformations of one segment into another.

Mutations and Phenotypes

A mutation is a change in the DNA sequence that can lead to alterations in gene function and, consequently, the phenotype of an organism. The phenotype refers to the observable characteristics or traits resulting from the interaction of the genotype with the environment. In the case of the extra sex combs mutant, the phenotype indicates a disruption in the normal expression of Hox genes, leading to the transformation of segments.

Gene Regulation

Gene regulation involves the mechanisms that control the expression of genes, determining when and how much of a gene product is made. In the context of Hox genes, regulatory genes like extra sex combs can influence the expression patterns of Hox genes, affecting segment identity. Understanding these regulatory interactions is crucial for deciphering how specific mutations can lead to distinct developmental outcomes.