Benedikt Hallgrimsson, PhD

1. The developmental genetic basis for phenotypic variation. Despite the tremendous progress made in recent years towards understanding fundamental developmental mechanisms, we know very little about the genetic or developmental causes of phenotypic variation within species or among related species. This is a central area for evolutionary biology as phenotypic variation is the raw material on which evolution acts. It is also an area that has important implications for understanding etiologically complex malformations such as cleft lip and palate. Such malformations occur at the extremes of multifactorial phenotypic distributions and must be understood within the same theoretical framework as other aspects of variation.

2. The developmental-genetic basis for variation in canalization, morphological integration, and developmental stability. How developmental systems modulate the translation of genetic into phenotypic variation is a fundamental question in current evolutionary developmental biology. It is clear that most genetic variation is cryptic, as evidence by the ubiquity of recessivity. It is also clear that the expression of genetic variation is dependent on genetic background and that pleiotropy is the norm. At the phenotypic level, the complexities of the genetic to phenotypic translation can be grouped into three phenomena. Canalization and developmental stability (DS) refer to the tendency of developmental processes to follow particular trajectories despite external or internal perturbation. Canalization is the tendency for development of a specific genotype to follow the same trajectory under different conditions (different environment or different genetic backgrounds) while DS is the tendency for development of a specific genotype to follow the same trajectory under the same conditions. Morphological integration refers to the tendency for structures to show correlated variation because they are affected by shared developmental processes. All three phenomena are emergent properties of developmental systems that complicate the translation of genetic to phenotypic variation.