140 CHARLES R. STOCKARD 



TESTING THE LOCATION OF THE GENE WHICH INDUCES 



ACHONDROPLASIA OF THE EXTREMITIES BY CROSSING THE 



DACHSHUND WITH THE BASSETHOUND AND WITH 



THE PEKINGESE 



The germ cells of the dog contain such a large number 

 of chromosomes more than forty that it is extremely dif- 

 ficult to associate a given gene influencing a certain character 

 with any individual chromosome. As previously mentioned, 

 no two characters among the many which we have studied 

 in the dog are clearly linked together in inheritance, although 

 certain of the head features in the bulldog have given some 

 indication of linkage. The difficulty in finding associated 

 characters is due, of course, to the high number of different 

 gene groups or chromosomes. 



We have, however, attempted to ascertain whether the 

 single gene necessary for achondroplasia of the extremities 

 is located in the same chromosomal pair in the different 

 breeds transmitting this character, particularly the basset- 

 hound, dachshund and Pekingese dog. If this single factor 

 dominant character is due to the presence of a specific gene 

 located in a given chromosomal pair in the bassethound, and 

 in the same or comparable chromosome of the dachshund, 

 then all individuals in the hybrid generations resulting from 

 a cross between these two breeds would constantly show 

 fully short achondroplasic extremities; there could be no 

 intermediate condition and no normal long legs. As far as 

 this character is concerned, the cross would be the same as 

 the pure line breeding. 



On the other hand, if the gene for this character is located 

 in different chromosomal pairs in the two breeds, the ex- 

 pectation for the second generation, F 2 , hybrids would be 

 three different classes of extremity lengths as indicated in 

 the diagram (text-fig. 1), in which we may assume that the 

 gene for achondroplasia in the mother is carried by the 

 round chromosomes, while in the father it is located in the 

 long chromosomes. Normal legs should appear among the 

 F 2 individuals, since one in sixteen would fail to receive a 



