64 CHARLES E. STOCKARD 



in some cases to know simply from the morphology and 

 without genetic tests whether an individual should be classed 

 as homozygous and extremely short, or mixed and inter- 

 mediate. In most cases, however, the diagnosis is quite clear 

 and certain. 



The crucial proof of the constitution in the questionable 

 cases must, of course, depend upon the genetic test, and these 

 we have made from time to time, as will be discussed below. 



THE ENHANCED EFFECTS FROM TWO ALLELOMORPHS FOR 



ACHONDROPLASIA AS COMPARED WITH THE EFFECTS 



FROM ONLY ONE SUCH GENE 



Mammals are so much more highly complex than are the 

 lower forms on which most genetic problems have been 

 analyzed that it may be permissible to discuss in connection 

 with these studies on dogs certain propositions that from 

 an orthodox genetic standpoint seem quite well established. 

 Such a proposition concerns the question of whether there 

 may be contamination of the gene for normal leg growth 

 after an association with the allel for achondroplasia. For 

 example, an F l bassethound-foxhound hybrid having short 

 legs will supposedly carry the allelomorphic genes s for short 

 and I for long legs in close contact in a chromosomal pair. 

 Will the gene for long, ?, or likewise the gene s for short, be 



PLATE 8 



EXPLANATION OF FIGURES 



Cross between the pure German shepherd and a mixed shepherd-bassethound- 

 foxhound female carrying two genes for long legs, one of which was associated 

 with the allelomorph for short in the chromosomal pairs of her bassethound- 

 foxhound father. Had the gene for long been contaminated by association with 

 the gene for short, half the offspring would show a decrease in leg length. All 

 hybrids from this mating were long logged. 



1 German shepherd 112 $. 



2 213 $, produced by mating a pure shepherd female to a bassethound-foxhound 

 male. 



3 Litter of nine hybrids (Nos. 356-364) produced by mating 213 $ to a 

 pure shepherd male. 



