A Semi-Lethal Mutation in Fowl Affecting Length of the Upper Beak and of the Long Bones.

N 1938 from matings of polydactylous fowl we found newly-hatched I chicks which had an abnormally short upper beak. In some of these chicks the beak gradually became normal, while others developed a crossbeak. The latter type has been referred to in an earlier publication (LANDAUER 1938, Postscript) as probably representing a new hereditary form of cross-beak in fowl. Further studies with this material revealed that the hatched chicks with abnormal beaks are the occasional survivors of a semi-lethal mutation. A report on the morphological expression and the hereditary transmission of this mutation is given in the following pages.