BASI'.S ()!• CIlANCr. 



logically, Griineberg has shown, for example, the common and 

 simple origin of a number o{ defects occurring together in the rat. 

 Distortion of the blood system and lungs, blockage of the nostrils, 

 inability to suckle and deformity of the bones of the forelegs, all 



Slight changes in Larynx 

 and Nose 



GENE 



Anomaly of Cartilage 



Thickened Ribs 



Spur on Deltoid Ridge of . * . 



Humerus _ Fixation of Thorax in Inspiration 



Fixation of Thoracic Vertebrae. 



Displacement of Thoracic Viscera 



Dilation of Lung Cavities and Passages 



/ \ 



Increased Resistance Arrest of Pevelopment 



Slow Suffocation in Pulmonary Circulation J Blocked Nostrils 



/ 7 Blunt Snout I 



/ Compensatory Overgrowth I Inability to Suckle 



I of Right Ventricle Faulty cutting of I 



Coma ^ \, Incisor Teeth | 



Capillary Bleeding Heart 1 Starvation 



Fig. 25. — The piciotropic effect of the grey-lethal gene in the rat (after Griineberg, 

 1938). 



these arise during development from a single abnormality in the 

 formation of the cartilage. The gene is single and pleiotropic 

 (Fig. 25). Genetically, we can get the evidence from the control 

 of dominance and the effects of other genes in modifying the action 

 of the one we are chiefly concerned with. The agouti series in the 

 mouse is a case in point. 



n6 



