Molecules, developmental modules, and phenotypes: a combinatorial approach to homology.
Most traditional views of homology rely on two unwarranted premises: the pervasively hierarchical nature of biology, inclusive of the levels of genes, development, and morphology and the linear mapping of genes onto developmental schedules and of developmental schedules onto phenotypes. These premises are only occasionally verified. Hierarchical behavior is negated by gene duplication and exon shuffling at the level of genes, by the coexistence of autonomous vs nonautonomous gene expression at the level of development, by ontogenetic repatterning at the level of morphology. The linearity of mapping of genes onto development is disturbed by genetic piracy, uncoupling of positional vs spatial control, and pleiotropy. The independence of developmental modules affects the mapping of development onto morphology and, finally, the peculiar topology of the epigenetic code affects the linearity of the gene to phenotype mapping. To cope with this complex behavior, a combinatorial approach to homology is recommended.
Minelli
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Department of Biology, University of Padova, Via Trieste 75, Padua, I 35121, Italy.
D000818:Animals; D002874:Chromosome Mapping; D004330:Drosophila / Q000235:genetics; D019143:Evolution, Molecular; D005091:Exons; D005815:Genetic Code; D008957:Models, Genetic; D005810:Multigene Family; D010641:Phenotype; D010802:Phylogeny; D017385:Sequence Homology