46 A NEW TYPE OF BRACHYPHALANGY IN MAN. 



is well worth noticing that in the single case where the possibility for 

 homozygous individuals was present in our material, a child, 115.2 

 9 C. F. H., was born who was a cripple " without fingers and toes" 

 and " with her whole osseous system in disorder." As described above 

 (pp. 28-29), this individual was unable to develop and died when one 

 year old. The possibility that we are here dealing with a homozygous 

 individual is pointed out above. 



From a medical point of view, this relation is of great importance. 

 The fact that an hereditary malformation in heterozygous individuals 

 is without any practical consequences by no means guarantees that the 

 malformation when the genes are homozygous will be as slight. In 

 similar cases a physician should warn affected members of such a 

 family against marrying each other, however trifling the malformation 

 may be. This attitude is fully justified by the facts established 

 through the experimental heredity work. 



The second point mentioned above a statement often met with in 

 publications concerning Mendelian heredity in man is that only 

 individuals who show the dominant character are able to transfer it 

 to their children. Here, too, a certain amount of reservation is neces- 

 sary, for the statement disregards entirely the fact that a great many 

 Mendelian characters are extremely variable in their somatic appear- 

 ance. This holds not only for recessive characters, but for dominant 

 characters as well. 



In Drosophila, for instance, numerous mutations are found that in 

 some individuals are very striking, but in others of exactly the same 

 genetic constitution are not visible at all. Between the striking appear- 

 ance of the character and its total failure of somatic manifestation a 

 series of variations are found. 



The dominant eye-character Star might here again with profit be 

 used as an illustration. In some individuals this character is very 

 marked in its appearance. The ommatidia are scattered around 

 without any regularity, the form and size of the eye is influenced and 

 the whole aspect is entirely different from that of the eye of the wild 

 fly. In other individuals the alterations caused by the Star gene are 

 so slight that it requires special training to use the character in experi- 

 mental work, and even a trained observer will meet cases where a 

 genetic test is necessary to decide whether the individual is Star or 

 not. Between these extremes all degrees in the manifestation of the 

 character are found. 



The parallelism with the character we are here dealing with in 

 human material is easily seen. Disregarding the question of two 

 types, to be discussed later, the fact is that some of the heterozygous 

 individuals show alterations of a nature so striking they they can not 

 escape even the most superficial observer. This was, for instance, the 

 case in the individuals 11.5 d", H5.4 rf 1 , 115.8 d 71 , and 11512.1 <? 



