Are homologous relationships constrained across biological levels?
Genetic and developmental features underlying homologous phenotypes can vary across taxa. My research on digit identity in birds and skinks illustrates that homologous phenotypes sometimes arise via diverse developmental processes. The avian wing digits are phenotypically conserved, but developmentally divergent. Our research confirmed an evolved digit identity transformation of avian wing digit I to embryological position 2 and discovered differences in Hoxd12 expression between the hand- and foot-plate that associate with digit transformations in birds and skinks. Current work focuses on the mechanistic bases of the evolved, wing-specific modification to Hoxd12 expression.