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mother, it must have been present in its father. If two men are alleged to
be the fathers of the child, and if one of them shows the iso-haemagglutino-
gen (isogen) A in. his blood and the other does not, the one who has the
isogen A must be the father. If both men have the isogen A, no definite
opinion regarding the paternity can be given. Either of them can be consi-
dered to be the father of the child as far as the evidence from the blood
groups is concerned.

The M and N hsemogens are also inherited and transmitted as Mendelian
dominants, and the following table gives the possible combinations of in-
heritance in the blood types : —

Types of Parents.
	Types of Possible Children.
	Types of Impossible Children.

 M x MIST M x N MN X MN MN X N" N x N"
	M M, MN MN M, N, MN, N, MN N
	N, MN N M, N None M, MMN

The following two rules are deduced from the above table : —

(i) The haemogens M and N cannot appear in the blood of a child unless
present in the blood of one or both parents.

(ii) A parent of type M cannot produce a type N child and a parent of
type N cannot produce a type M child.

The Rh haemogen is also determined by heredity. Greval32 has prepared
the following table showing the possible and impossible children occurring
in the Rh blood types : —

Types of Parents.
	Types of Possible Children.
	Types of Impossible Children.

Eh-f x Bh+ Eh-f X Rk — Eh— x &h—
	Eh-f , Eh— Eh-h Eh— Eh—
	Eh i-

The following two rules emerge from the above table: —

(i) Rh negative parents cannot produce an Rh positive offspring.

(ii) Rh positive and mixed parents can produce Rh positive and Rh
negative offspring.

Blood group testing should always be performed first and would be quite
sufficient in many instances. The advantage of testing the M and N types
is that these have no relation to the primary blood groups. Thus, two
individuals, for example, two possible fathers, may belong to the same pri-
mary Wood group, and yet may have a different content of the haemogens
M and N, The application of the Rh tests is also necessary, as it materially
increases the chances of exclusion of parentage. A case 33 is reported in
which an alleged father was excluded by the Rh tests, although ABO group-
ing, sub-grouping, and MN test were not conclusive.

The question of disputed paternity arises in court in the following
circumstances : —

32.   Ind. Meet. Gaz., April 1945, p. 204.

33.   Wiener, Sonn and Belkin, Jour. Exper. Med., Vol. 79, 1944, p. 235,