Application of DNA·VIEW to a paternity case

Toshiko Sawaguchi, Charles Brenner, Akiko Sawaguchi

13 December 1997
(Poster from the Japanese DNA Polymorphism meeting, Nagasaki, 4 December 1997)

family tree for cousin case Family tree for a complicated cousin case


Mr. A and Mrs. C, cousins, may or may not be the parents of Mr. B.


Genetic typing was performed in several DNA and serological systems for the six individuals B, C, E, F, G, H, who are drawn with thick lines.

Mr. A was not available for testing so his types must be inferred indirectly from those of his half-brother and half-sister (G and H), of his child E from another cousin (Mrs. D), and from the types of his other cousins F and B as shown.


The mother-child relation between Mrs. C and Mr. B is easily analysed as a fatherless (logically equivalent to motherless) maternity case using the PATER program.

The possible father-child relationship between Mr. A and B is investigated with the Symbolic Kinship Program. The Kinship program is also used to analyse the possible trio relationship among Mr. A, Mrs. C, and B.

Maternity analysis

child B -?- woman Mrs. C
Maternity 99.9%
16 blood groups
"fatherless" computation using just 2 people
As shown by the fatherless maternity report from PATER, the maternity index favoring maternity by Mrs. C is 2570. Therefore the maternity of Mrs. C is, as Hummel would say, "practically proven."

Paternity analysis (trio)

Man A. -?- child B -+- woman Mrs. C
Paternity 0.6%
9 simple systems
Kinship program, use types of several relatives
In view of the apparent maternity of Mrs. C, it seems natural to ask whether, assuming Mrs. C is the mother of B, is Mr. A the father?

To this end the Symbolic Kinship Program is used to make an analysis (details and exhibits) which makes use of all the typing data from the various relatives.

In summary, the combined paternity index across all computed loci is about 1/200. That is, the liklihood ratio favoring non-paternity is about 200.

Using the verbal predicates of Hummel, the paternity of Mr. A is "extremely unlikely" if Mrs. C is the mother.

Paternity analysis (motherless)

Man A. -?- child B
Paternity 4%
8 simple systems
Kinship program, use types of several relatives
That would seem to wrap it up. If Mrs. C is "practically proven" to be the mother, and Mr. A is "extremely unlikely" to be the father if she is, then how can the possibility that he is the father be anything but slim?

The answer is that since the verbal predicates have an unjustified assumption of "equal priors" built into them, the reasoning is not air-tight. This point is discussed on the page "Man, woman, and child."

Therefore, just to be careful, a further analysis was done to test the paternity of Mr. A, assuming that Mrs. C is not the mother. In summary, the likelihood ratio came to 1/23, suggesting that paternity is "very unlikely."


Man A. xxx child B +++ Mrs.C

Comments? Questions? Disputes?

Links: Forensic mathematics home page.