Is function of the Drosophila homeotic gene Ultrabithorax canalized?
Genetic variation affecting the expressivity of an amorphic allele of the homeotic gene Ultrabithorax, (Ubx1) was characterized after 11 generations of introgression into 29 different isofemale lines. Heterozygotes display a range of haploinsufficient phenotypes, from overlap with wild-type halteres to dramatic transformations such as a 50% increase in area and the presence of over 20 bristles on the anterior margin of each haltere. In both the wild-type and mutant genetic backgrounds, there is moderate genetic variance and low environmental variance/developmental asymmetry, as expected of a trait under stabilizing selection pressure. Surprisingly, there is little evidence that mutant halteres are more variable than wild-type ones, so it is unclear that haltere development is also canalized. The correlation between wild-type and Ubx haltere size is very low, indicating that interactions among modifiers of Ubx are complex, and in some cases sex-specific. The potential quantitative genetic contributions of homeotic genes to appendage morphology are discussed, noting that population-level effects of variation in key regulatory genes may be prevalent and complex but cannot be readily extrapolated to macroevolutionary diversification.
Gibson
G
G
Department of Biology, The University of Michigan, Ann Arbor 48109-1048, USA. ggibson@umich.edu
van Helden
S
S
D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics*; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000033:anatomy & histology / Q000235:genetics*; D005260:Female; D005801:Genes, Homeobox; D017344:Genes, Insect; D014644:Genetic Variation; D018398:Homeodomain Proteins / Q000235:genetics*; D008297:Male; D014157:Transcription Factors
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; C066177:Ubx protein, Drosophila