Evolution of pleiotropy and morphological integration

The underlying genotypic basis of phenotypic variability is often referred to as the genetic architecture of the phenotype. Genetic architecture plays a critical role in determining phenotypic evolution through its effects on patterns of genetic variation. It is specified by the number of loci affecting the trait, the additive and dominance genotypic values at single loci (Falconer and Mackay, 1996), the locus-specific range of pleiotropic effects, and the epistatic genotypic values for locus pairs (Cheverud and Routman, 1995; Routman and Cheverud, 1997). Genetic architecture is mostly considered constant in quantitative genetic models. However, it is also clear that genetic architecture may be genetically variable and evolve. The pattern of pleiotropic effects has been suggested to follow functional and/or developmental units and thus the effects of single genetic regions are restricted to developmentally or functionally related traits. Such modular organization of the genotype-phenotype map is supposed to result from selection favouring the evolvability of the complex phenotype (Wagner and Altenberg, 1996). However, if the modularity evolves, it must be genetically variable. The underlying idea of proposed research is to measure genetic variation in the scope and extent of pleiotropy. Just as Quantitative Trait Locus (QTL) -based research has opened the way to studies of the genetic architecture of complex traits it provides the basis for the studies on variability and evolution of genetic architecture (Cheverud and Routman, 1993; Ehrich et al., 2003; Cheverud et al. 2004). The proposed study utilizes the morphological and genetic data on well studied morphological system mouse mandible. The data have been compiled in the course of numerous previous studies of different morphological and evolutionary aspects. The main objectives of the study concern the differential epistasis and its effects upon the variance/covariance matrix of the mouse mandible.