Chapter 9 - The Origin of Evolutionarily Novel Genes and Evolution of New Functions and Structural Complexity in Multicellular Organisms

Abstract

The origin of evolutionarily novel genes is connected with the origin and evolution of the novel organismal functions and the increase in morphological complexity of multicellular organisms. Novel genes acquire new or altered functions. Different modes of gene origin – gene duplication, exon shuffling and de novo origin – are connected with somewhat different ways of acquisition of new functions. The duplicate genes can acquire new functions by neofunctionalization, i.e. the origin of an entirely new function, and by subfunctionalization, when each of two genes retains only a subset of original functions. Exon shuffling leads to novel combinations of already existing functions. De novo–originated genes should have some novel, previously non-existent functions. These functions fit into developmental or terminal differentiation classes of functions. Correlation of phylogenetic differences at later ontogenetic stages with the expression of newly evolved genes and other evidence support the role of novel genes in the origin of evolutionary innovations and morphological novelties. The extra cell masses are needed for the expression of novel genes and the origin of innovations.