Robustness in development allows for the accumulation of genetically based variation in expression. However, this variation is usually examined in response to large perturbations, and examination of this variation has been limited to being spatial, or quantitative, but because of technical restrictions not both. Here we bridge these gaps by investigating replicated quantitative spatial gene expression using rigorous statistical models, in different genotypes, sexes, and species (Drosophila melanogaster and D. simulans). Using this type of quantitative approach with molecular developmental data allows for comparison among conditions, such as different genetic backgrounds. We apply this approach to the morphogenetic furrow, a wave of differentiation that patterns the developing eye disc. Within the morphogenetic furrow, we focus on four genes, hairy, atonal, hedgehog, and Delta. Hybridization chain reaction quantitatively measures spatial gene expression, co‐staining for all four genes simultaneously. We find considerable variation in the spatial expression pattern of these genes in the eye between species, genotypes, and sexes. We also find that there has been evolution of the regulatory relationship between these genes, and that their spatial interrelationships have evolved between species. This variation has no phenotypic effect, and could be buffered by network thresholds or compensation from other genes. Both of these mechanisms could potentially be contributing to long term developmental systems drift.

中文翻译：

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定量空间基因表达的新方法揭示了正在发展的果蝇眼中的遗传随机性。

发展中的稳健性允许积累基于遗传的表达变异。但是，通常会根据较大的扰动来检查这种变化，并且对该变化的检查仅限于空间的或定量的，但由于技术限制，不能同时考虑这两种情况。在这里，我们通过研究使用严格的统计模型，在不同的基因型，性别和物种（果蝇（Drosophila melanogaster和D. simulans））。将这种定量方法与分子发育数据一起使用，可以在各种条件（例如不同的遗传背景）之间进行比较。我们将这种方法应用于形态发生的犁沟，这是一股分化的波，其形成了发育中的眼球。在形态发生犁沟中，我们关注四个基因，毛状，无齿，刺猬和三角洲。杂交链反应定量测量空间基因表达，同时同时对所有四个基因进行染色。我们发现这些基因在眼睛中的空间表达模式在物种，基因型和性别之间存在很大差异。我们还发现这些基因之间的调节关系已经进化，并且它们在物种之间的空间相互关系也已经进化。这种变异没有表型效应，可以被网络阈值或其他基因的补偿所缓冲。这两种机制都可能导致长期的开发系统漂移。