Functional Divergence of the and Paralogs.

and encode paralogous transcription factors found as a closely linked tandem duplication within holometabolous insects. mutants segment normally, then fail to maintain their segments. Loss of is viable, while loss of both genes results in asegmental larvae. Surprisingly, the knockdown of can result in the loss or fusion of the entire abdomen and knockdowns in show variable degrees of segmental loss. The consequence of losing or knocking down both paralogs on embryogenesis has not been studied beyond . To further investigate the relative functions of each paralog and the mechanism behind the segmental loss, double and single knockdowns of and were analyzed. The most common cuticular phenotype of the double knockdowns was small, limbless, and open dorsally, with all but a single, segmentally iterated row of bristles. Less severe knockdowns had fused segments and reduced appendages. The paralogs appear to act synergistically: the knockdown of either gene alone was typically less severe, with all limbs present, whereas the most extreme single knockdowns mimic the most severe double knockdown phenotype. Morphological abnormalities unique to either single gene knockdown were not found. expression was not affected in the knockdowns, but expression was unexpectedly increased midway through development. Thus, while the segmental expression of is broadly conserved within insects, the functions of and are evolving independently in different lineages.