GENETIC TYPE AND THE ENDOCRINES 359 



at this time to recall the inheritance of achondroplasia in the 

 extremities since it differs so largely in its simple genetic 

 basis from the more complex genetics for the closely similar 

 growth phenomena of basicranial achondroplasia and the 

 reduction of growth in the jaws. In plate 34 (figs. 1-4), the 

 Pekingese is seen to have very short and typically bent front 

 legs in contrast with the long, straight and slender legs of 

 the Saluki. The two F x hybrids (figs. 5 and 6) have both 

 developed short, bent legs resembling those of the Pekingese, 

 although not fully as short. This strongly indicates that 

 short legs result from the presence of a simple dominant 

 factor, and is convincingly demonstrated by the F 2 hybrids 

 (figs. 7-11). Figures 9-11 are homozygous for short, bent 

 Pekingese legs; figure 8 is heterozygous for the short factor 

 and shows legs of intermediate shortness as in the hetero- 

 zygous Fj ; while figure 7 has the recessive long, straight 

 legs and contains no factor for short legs, even though not 

 constitutionally the slender Saluki type. 



The Pekingese round head and flattened face with extremely 

 reduced jaws and muzzle is a complex arrangement involving 

 a number of modified characters, each of which may have 

 its own independent genetic basis. And the inheritance of 

 each of the different elements in this complex of characters 

 may be compared to the inheritance of the achondroplasic 

 leg. Tlie head of the Pekingese is not to be thought of as 

 a mass character inherited through multiple factors, but 

 rather as a multiplex of characters whose separate elements 

 are independently influenced by different genetic factors, 

 some dominant and others recessive to the allelomorphs for 

 normal expression. And yet as one studies the structural 

 modifications in these breeds and their hybrids it becomes 

 more and more evident that simple chondrodystrophy is the 

 common growth modification or deficiency underlying the 

 development of most of these seemingly different structural 

 distortions. The surprising fact then arises that this common 

 disturbance, dystrophy in cartilage formation, may be minute- 



