Biomedical subjects
Publications and source records attributed to A Palsson.
Developmental geneticists' contribution to the study of the evolution of morphological divergence has proceeded along two lines: comparative analysis of gene expression and quantitative genetics. Recent studies highlight how complementation tests between species can bridge the gap between these approaches.
Quantitative complementation tests provide a quick test of the hypothesis that a particular gene contributes to segregating phenotypic variation. A set of wild-type alleles is assayed for variation in their ability to complement the degree of dominance of the quantitative effect of a loss of function allele. Analysis of 15 loci known to be involved in wing patterning in Drosophila melanogaster suggests that the genes decapentaplegic, thickveins, EGFR, argos and hedgehog, each of which are involved in secreted growth factor signaling, may contribute to wing shape variation. The phenotype of one deficiency, Df(2R)Px2, which removes blistered/Plexate, is also highly sensitive to the wild-type genetic background and at intermediate expressivity reveals six ectopic veins. These form in the same locations as a projection of the ancestral pattern of dipteran wing veins on- to the D. melanogaster wing. This atavistic phenotype indicates that the wing vein prepatterning mechanism can be conserved in highly derived species, and implies that homoplasic venation patterns may be produced by derepression of vein primordia.
Two composite multiple regression-interval mapping analyses were performed to identify candidate quantitative trait loci (QTL) affecting components of wing shape in Drosophila melanogaster defined by eight relative warp-based measures. A recombinant inbred line design was used to map QTL for the shape of two intervein regions in the anterior compartment of the wing, using a high resolution map of retrotransposon insertion sites between Oregon-R and Russian 2b. A total of 35 QTL representing up to 23 different loci were identified, many of which are located near components of the epidermal growth factor-Ras signal transduction pathway that regulates vein vs. intervein decision making and vein placement. Over one-half of the loci were detected in both sexes, and just under one-half were detected at two different growth temperatures. Different loci were found to affect aspects of shape in each intervein region, confirming that the shape of the whole wing should be regarded as a compound trait composed of several developmental units. In addition, a reciprocal backcross design was used to map QTL affecting shape in the posterior compartment of the wings of 831 flies, using a molecular map of 16 allele-specific oligohybridization single nucleotide polymorphism (SNP) markers between two divergent inbred lines. A total of 13 QTL were detected and shown to have generally additive effects on separable components of shape, in both sexes. By contrast, 8 QTL that affected wing size in these backcrosses were nearly dominant in their effects. The results confirm at the genetic level that wing shape is regulated independent of wing size and set up the hypothesis that wing shape is regulated in part through the regulation of the length and positioning of wing veins, involving quantitative regulation of the activity of secreted growth factors.