LINKAGE 695 



of connection must be distinguished ; in the first, two characters 

 are always inherited together, and are quite inseparable. Here, 

 a factor is having more than one phenotypic effect, and may be 

 called pleiotropic. Generally, the multiple results follow from a 



GENE 



1 



Slightchanges in Larynx 

 and Nose 



Spur on Deltoid Ridge of 

 Humerus 



Anomaly of Cartilage 



1 



Thickened Ribs 



I 



Fixation of Thorax in inspiration 



Narrow 

 Tracheae 



Fixation of Thoracic Vertebrae. 



Displacement of Thoracic Viscera 



1 



Slow Suffocation 



coma 



Dilation of Lung Cavities and Passages 



/ \ 



Increased Resistance Arrest of Development 



in Pulmonary Circulation I 



/ Blunt Snout 



Compensatory Overgrowth I 



of Right Ventricle Faulty cutting of 



y V Incisor Teeth 



Blocked Nostrils 



\ 



Inability to Suckle 



Capillary Bleeding 

 in Lungs 



Heart 

 Failure 



t 



I 



Starvation 



I 



Feeding Difficulties 



DEATH 



Fig. 542.— The pleiotropic efiEect of a single gene, grey-lethal, in the rat.— From 

 Darlington and Mather, The Elements of Genetics, 1949. AUen & Unwin, London. 

 After Griineberg. 



single initial change, as in a large number of anatomical and 

 physiological defects in the rat, which were traced to a single 

 anomaly in the formation of cartilage (Fig. 542), but it is not 

 impossible that sometimes a single factor may determine more 

 than one reaction, the effects of which would then be unrelated 

 except through their cause. More often, there is merely a pre- 

 ponderance of one type of combination of the two characters. 



