58 CHARLES R. STOCKARD 



shepherd, II, while the achondroplasic intermediate-short leg 

 results from half bassethound and half shepherd effects, Is. 

 These reactions accord with the principles of Mendelian segre- 

 gation of characters in inheritance and are mentioned here 

 since many workers in fields bearing on other phases of this 

 investigation are unfamiliar with genetic conceptions. 



In the smallest of the backcross litters there were only 

 two individuals, and by chance one of these was long legged 

 and one short legged. Plate 5 illustrates the contrast in leg 

 length between these litter mates, 652 $ II and 653 9 si, when 

 4 months old (fig. 3) and as adults (fig. 5), with the parent 

 types pictured above. The skeletons from these two dogs 

 in front and side views are shown in plate 6. Comparing 

 these two skeletons vividly illustrates the effect of the single 

 allel for achondroplasia as derived from the bassethound. 

 In figure 3 of plate 6 the very short and bent tibia from 

 653 $ is shown on the left and the long and almost straight 

 line tibia from the brother on the right. The contrast between 

 the growth patterns in these two bones is extreme and it is 

 surprising to realize that in a mammal the presence of only 

 one modified gene may give rise to so great a distortion in 

 form and size. The difference between the achondroplasic 

 short and twisted humerus and the normal humerus is shown 

 by figure 4. This modification in growth is strictly confined 

 to the skeleton of the extremities ; the axial skeletons of these 

 two animals are alike and normal, as is clearly shown by the 

 lateral aspects in figures 5 and 6 of plate 6. 



PLATE 5 



EXPLANATION OP FIGURES 



Backcross of the F, German shepherd-bassethomul having intermediate legs 

 with the pure long legged shepherd parent. The expectancy here is equal numbers 

 of intermediate and long legged hybrids. 



1 German shepherd 118 $. 



2 F t 251 <?. 



3 Backcross hybrids 653 $ (intermediate legs) and 652 (long legs) at 4 

 months. 



5 Same two dogs at 18 months of age. 



4 Backcross 501 <$. The head and body of this animal are very like the pure 

 shepherd, but the legs are achoudroplasic like the bassethound. Note the erect 

 ears as in the shepherd parent. 



