88 CHARLES R. STOCKARD 



The double short, ss, backcross bassethoiuid male 858, at 

 the right in plate 16, was mated to an intermediate sister, 

 860, the center dog in the same group. These two animals 

 are shown in a side view photograph in plate 17 (fig. 1), and 

 in this position the two different degrees of leg condition 

 are clearly contrasted. No. 860 9 has a short leg with a twist 

 at the wrist, indicated by the bulge just above the white foot, 

 while the legs of 858 $ are even shorter, and the top of his 

 head is but slightly higher than the sister's shoulder. In 

 the male, the knob at the wrists is also more pronounced. On 

 the basis of the morphological appearance of the legs of these 

 two animals, they were diagnosed for the achondroplasia re- 

 action as of the genotypes si and ss. If this deduction from 

 the phenotypic differences is correct, then their mating should 

 produce only si and ss individuals in about equal numbers. 

 Xo long legs, 11, should appear unless the diagnosis for ss is 

 incorrect and si the correct interpretation. 



A litter of five puppies was whelped from this mating, 

 three males and two females. Two puppies had very short 

 legs like those of the father, and three had legs of a lesser 

 degree of shortness like those of the mother. In figure 2 of 

 plate 17, four of the five animals are shown. The two dogs 

 in the center have legs of intermediate shortness, si, and the 

 left and right animals are very low and short legged, .95. 

 This result proves the correctness of our diagnosis of the 

 degree of chondrodystrophy in the legs of the parents. 



The above mating, along with the comparable one between 

 the backcross Saluki hybrids illustrated in plate 15, proves 

 conclusively that it is possible to distinguish the difference 

 between growth deformities of the legs resulting from the 

 presence of the one or the two genes for the modification, 

 and that the growth expression when the allelomorphs are 

 heterozygous differs from that when homozygous. 



A consideration of the skeletons of the extremities from 

 the animals in these crosses further substantiates the above 

 interpretations. This will be fully illustrated and discussed 

 in a chapter following the presentation of the leg conditions 

 in the bassethound and English bulldog cross. 



