Sec. 3.1 THE DETERMINATION OF PROBABILITIES 61 



The information given previously on blood groups can be sum- 

 marized as follows: 



Blood Typing System 



I(A-B) II(M-N) III(P) IV(Rh) 



O/O = group O M/M = type M P/P Rh/Rh 



or or 



A/0 N/N = type N P/p = type P+ Rh/rh = type Rh+ 



or 



A/A = group A M/N = type MN p/p = type P- rh/rh = type Rh- 



B/0 

 or 

 B/B = group B 



A/B = group AB 



It is seen that there are 4 X 3 X 2 X 2 = 48 mutually exclusive 

 and serologically distinguishable blood classifications, even with the 

 simplified groups discussed herein. By using all the known sub- 

 groups of blood types, there are many more distinguishable and mutu- 

 ally exclusive classifications of human bloods. The availability of 

 these classifications has been helpful in legal cases involving dis- 

 puted parentage, heirship claims when alleged maternity is doubted, 

 identification of blood stains, genetic studies, anthropological inves- 

 tigations, and the identification of corpses when other methods have 

 failed. 



Apparently the chief use of blood types in legal cases occurs when 

 one can prove the impossibility of an allegation. For example, an 

 O-type father and an AB-type mother cannot (under the informa- 

 tion set forth above) have an O-type child. Or, as another case, if 

 an accused person has blood stains on his clothing and claims that 

 they resulted from his having had a nosebleed, the finding that his 

 blood is A, M whereas the stains are A, N would disprove his claim. 



PROBLEMS 



1. What is the probability that a wife with type A blood and a husband with 

 type B blood will have three children whose blood types all are O? 



2. Suppose that a husband has type A blood and that his wife's blood group 

 is AB. What is the most likely type of blood for their first child under the 

 assumptions made in Table 3.12? What type is impossible? Ans. A, O. 



3. If the parents of problem 2 claim five children all of blood type B, would 

 you doubt the blood types or, perhaps, the alleged parentage? Give probability 

 argument. 



