200 READINGS IN BIOLOGICAL SCIENCE 



The first of these practical applications involves the physician, who may 

 find a knowledge of human heredity of value in diagnosis, especially early 

 dia^osis. Instances are on record in the medical literature involving 

 telangiectasis, polycythemia vera, spina bifida, orthoglycemic glycosuria, 

 multiple exostoses and others, where the proper diagnosis was not made 

 until the genetic background was taken into account. 



A second practical appHcation of a knowledge of human heredit\' con- 

 sists in the outlining of preventive measures as a result of the examination 

 of the family histor\- of the patient. Tests for pre-clinical and laboratory 

 si?ns of a disease which has a genetic basis may be made in the relatives 

 of affected individuals, and proper preventive measures instituted where 

 indicated, before the condition becomes acute. This is being done by 

 many physicians in cases of pernicious anemia and its antecedent achlor- 

 hydria, in certain t\-pes of cancer, in hemolytic icterus, in hypertension, 

 in diabetes and in other cases where a genetic background is known. 



A third practical application involves the lawyer. In recent years the 

 heredit\- of several substances (antigens) found in human red blood cells 

 has been carefully worked out. On the basis of this knowledge a man 

 falsely accused in a paternity- case may be cleared of the charge in cer- 

 tain instances. 



As a fourth practical application of a knowledge of human heredity, 

 such knowledge may furnish the basis for advice on prospective mar- 

 riages. It is a common experience for the geneticist to be asked, "\^^hat 

 are the chances that this trait which is in my family background will ap- 

 pear in my children?" Sometimes it is a trait which the individual may 

 be desirous of having in his children, such as musical ability, intelligence 

 or red hair. At other times it may be an unwanted trait such as feeble- 

 mindedness, dementia praecox or deaf-mutism. When such questions are 

 asked, the geneticist must call on his knowledge of the trait concerned, the 

 possible genetic basis, the variabilit\' caused by different environments, 

 and from this composite picture reach some ans^ver. Frequently the 

 answer must be vamae and unsatisfactor\' because there is not enough 

 exact knowledge concerning the parts played by heredity and by en- 

 vironment in the production of the trait. Sometimes, however, where 

 such knowledge is at hand, valuable information may be given. 



In a recent case a hemophilic patient with a tj'pical family history- of 

 the disease stated that his three daughters had not been told the nature of 

 his affliction, nor were they to be told, since he was ashamed of the 

 hereditary* blemish, as he considered it. Yet if these daughters marry, half 

 their sons will be expected to have hemophilia, a condition which proves 

 fatal in childhood in the majority of instances. Advance knowledge of the 

 chances of hemophilia in these families would at the ver\* least make it 

 possible for the mothers of sons to have every-thing in readiness for an 

 emergency transfusion at any time. 



