142 CHARLES R. STOCKARD 



chromosome carrying the gene for achondroplasia (A -f- a) ; 

 four in sixteen would receive only one chromosome carrying 

 the gene (A + c, A -f d, C + a, D + a) and would therefore 

 show the intermediate condition; while all others of this 

 generation would show fully achondroplasia extremities due 

 to the presence of at least two genes for the condition. 

 There is also the possibility that some of these animals, in 

 fact, a fourth of them, would carry three such genes (B + c, 

 B + d, C -+- b, D -j- b) and one in sixteen, being homozygous 

 through two pairs of chromosomes (one pair from each parent 

 stock) could have four genes for achondroplasia (B-f-b). 

 These animals with an excessive number of genes for achon- 

 droplasia might give rise to exaggerations of the deformity 

 and be almost or completely legless. Therefore, the expecta- 

 tions for the transmission of this deformity to the hybrids, 

 provided the modifying genes were located in different 

 chromosomes in the two breeds, would be exactly the same 

 as in any case of a character dependent for its transmission 

 upon genes in two different chromosomes. The long legs 

 would appear as a double factor recessive in the one F« out 

 of sixteen (A -4- a) which failed to receive a chromosome 

 carrying the gene for short from either of the two responsible 

 chromosomal pairs. 



The results of crossing the bassethound and the dachshund 

 do not show such different varieties in extremity forms. 

 All the hybrids in both the first and second generations were 

 uniformly short with achondroplasia extremities. 



Two slightly related bassethound bitches were bred to 

 two distantly related dachshund males, and litters of eight 

 and five F, puppies were whelped. Animals from these two 

 F, litters were mated in various combinations and produced 

 fifty-four F._, offspring which showed various conditions of 

 size, color patterns, etc. Some of these will be referred to 

 later. But the achondroplasia short leg character was uni- 

 formly consistent in its expression in the fifty-four F L . ani- 

 mals. All were diagnosed as fully short and were apparently 

 homozygous individuals, indicating that the genes for achon- 



