124 CHARLES R. STOCKARD 



LOCALIZED ACHONDROPLASIA IN THE EXTREMITIES OF THE 

 DACHSHUND AND THE PEKINGESE 



The reader no doubt appreciates by this time that we have 

 fully tested the inheritance of short achondroplasic growth 

 in the extremities as transmitted by the bassethound when 

 hybridized with widely different stocks. However, a question 

 still remains whether the short leg condition found in other 

 breeds, such as the dachshund and the Pekingese, is trans- 

 mitted in the same genetic fashion. We have mentioned in 

 an earlier section that the short leg deformity appeared very 

 early in the history of the dog and that a low turnspit-like 

 animal probably arose independently in several widely sepa- 

 rated parts of the world. Did this modification of the legs 

 always arise from a single point mutation which affected 

 the same gene in all breeds or races! It is a matter of con- 

 siderable genetic importance to learn whether in the complex 

 constitution of higher mammals, such as the dog, there is a 

 tendency for the same mutation to appear in different stocks 

 and, after arising, to react in inheritance in only one way 

 when paired with non-mutant allelomorphs. 



If each gene in a series is a different complex protein 

 molecule, then a given gene which exerts its most noticeable 

 influence on a particular character may be very closely or 

 exactly the same kind of compound in all the species in which 

 this character occurs. In other words, exactly the same gene 

 probably exists in many different animals and functions in 

 a similar way in all of them. If the gene is somewhat unstable 

 in composition and tends to mutate by shifting or dropping 

 a secondary or side chain compound, one may imagine that 

 the same modification would repeatedly tend to occur at 

 the least stable point rather than at a different point each 

 time. Chemical compounds usually build up or break down 

 by definite steps instead of changing first in one way and 

 then in another. The same mutation has been found to 

 occur in many different stocks of the fruit fly, DrosophUa. 

 Against the above supposition, however, is the fact that a 



