The Concepts of Variable Expressivity and Penetrance of the Jaspe Mutation in the Species Serinus canaria

The Jaspe mutation represents one of the most recent and complex innovations in the genetics of the domestic canary (Serinus canaria). Introduced through interspecific hybridization from the Eurasian siskin (Spinus spinus) and the blackheaded siskin (Spinus magellanicus), it is characterized by a partially dominant autosomal behaviour, with distinct phenotypes in heterozygotes (single factor) and homozygotes (double factor).The aim of this paper is to analyse the penetrance and variable expressivity of the Jaspe mutation, integrating fundamental concepts of Mendelian and nonMendelian genetics, and comparing the mutation with other known dilutions in canary breeding (namely Pastel and Greywing).The analysis shows that the mutation exhibits high penetrance but wide phenotypic variability, likely influenced by modifier genes, the genetic background of the founding lines, and epigenetic interactions. Implications for selection, phenotypic standardization, and future classification within FOI (Italian Ornithological Federation) and COM (World Ornithological Confederation) standards are discussed.