524 Animal Biology 



Chapter 34 (Heredity-Genetics) (Figs. 347 and 352 to 356). The reader 

 is warned not to jump at erroneous conclusions in his attempt to inter- 

 pret the inheritance of some of his own traits or those of famihes with 

 which he is more or less familiar. Careful interpretations by experienced 

 geneticists should be followed rather than depending upon our own 

 limited knowledge. 



Some of the most important data in human heredity are concerned 

 with the inheritance of specific blood groups. It is known that blood 

 from certain individuals when mixed frequently results in an agglutina- 

 tion (clumping) of the red blood corpuscles. Four types of human blood 

 are known as Groups A, B, AB, and O. Agglutination occurs when 

 certain groups are mixed and not when others are mixed. Agglutination 

 of human blood depends upon the presence of ( 1 ) the specific substance 

 known as the agglutinogen (a type of antigen) in the red blood corpus- 

 cles and (2) the specific substance known as the agglutinin (a type of 

 antibody) in the blood plasma. Both of these are necessary for a blood to 

 agglutinate, so naturally both cannot occur in the same person or his 

 blood would agglutinate in his blood vessels. The two inheritable ag- 

 glutinogens are known as A and B in man. Hence the following human 

 blood groups are possible: An individual of group A has agglutinogen 

 A in his red blood corpuscles; group B has agglutinogen B; group AB has 

 both agglutinogens A and B; group O has neither agglutinogen. Which- 

 ever agglutinogen an individual has in his red blood corpuscles, the cor- 

 responding agglutinin (antibody) is absent in his blood plasma. When 

 an agglutinogen is absent in his erythrocytes, the corresponding agglutinin 

 is present in his plasma. A summary of the blood groups, their agglutino- 

 gens, agglutinins, etc., is given in the following table: 



Human Blood Groups 



Persons of type O are often called "universal donors" because their blood 

 may be given safely without agglutination to any other person; persons of 



