Final answer:
Hox genes control gene expression by regulation of DNA transcription, and they are pivotal for the correct development of body parts in multicellular organisms such as flies.
Step-by-step explanation:
Gene expression in eukaryotes can be regulated at various levels. Certain mutations in flies may cause them to develop an extra set of legs or wings. Hox genes, which determine the formation and arrangement of body parts in multicellular organisms, control gene expression by regulation of DNA transcription.
In eukaryotic cells, gene expression can be regulated at different stages, from DNA transcription to mRNA translation and protein modification. Homeobox genes, particularly Hox genes, play a crucial role during the development of multicellular organisms by controlling where and when specific sets of genes are activated, thus determining the placement of body parts such as limbs and wings.
Regulation of gene expression is critical to ensure that proteins are synthesized at the right time and place, which is fundamental for the proper development and function of all living organisms.