578 GENETICS AND EVOLUTION 



Table 12. THE INHERITANCE OF THE HUMAN BLOOD GROUPS 



two, but neither a^ nor a^ is dominant to the other; each produces its 

 characteristic agglutinogen independently of the other. Transfusions of 

 blood from one person to another are successful only when the two 

 bloods are compatible, when the agglutinins in the plasma of the re- 

 cipient do not react with the agglutinogens in the red cells of the donor 

 to cause agglutination, clumpmg of the red cells. People with type O 

 blood (no agglutinogens in their red cells) are known as "universal 

 donors"; their blood can be transfused into the veins of persons with 

 any of these blood groups. People with type AB blood are called "uni- 

 versal recipients"; they have no agglutinins in the plasma and hence 

 their plasma will not cause agglutination of the red cells from any per- 

 son. 



Since blood types are inherited, and do not change in a person's 

 lifetime, they are useful indicators of parentage. In cases of disputed 

 parentage, genetic evidence can show only that a certain man or woman 

 could be the parent of a particular child, and never that he is the parent. 

 In certain circumstances, however, the genetic evidence can definitely 

 exclude a particular man or woman as the parent of a given child. Thus, 

 if a child of blood group A is born to a type O woman, no man with 

 type O or type B blood could be its father (Table 13). 



There are now eleven different sets of blood groups, inherited by 

 different pairs of genes, all of which are helpful in establishing paternity. 

 The most important of these are the Rh alleles which determine the 



Table 13. EXCLUSION OF PATERNITY BASED ON BLOOD TYPES 



