Morphogenetic studies of the rabbit XXXVI. Effect of gene and genome interaction on homeotic variation

Study of the homeotic shifts of vertebral borders as affected by the Da gene when on two different genetic backgrounds shows that the effects of both gene and genome are distinguishable. The Da in either one or two doses shifts both thoracolumbar and lumbosacral borders forward, particularly the former. The effect of the DA genome is in the same direction, but significantly greater, and the two combined are additive. The effect of the III Da genome, by contrast, is in the posterior direction and epistatic. It suppresses and tends to shift the localization of Da effect posteriorly. Significant differences between borders when considered separately and in relation to each other indicate differences of interaction between gene and genome. The fact that the only significant difference in the three way comparisons of border, genotype, and genome is between the Da / + genotypes of III Da and DA as a manifestation of overdominance can be discounted because of the differences in border interaction. As reference points defining the relative size and position of the thoracic and lumbar regions, these borders reveal the activity of gene and genome to be an alteration of the relative size and position of the growth gradients of these two regions rather than a direct gene specific morphology.