Paternity Disputes in Forensic Medicine
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Direct answer
Blood groups can exclude a father; they can never name one. A putative father of group O cannot parent a group AB child, and an AB parent cannot pass an O allele — exclusions like these are absolute, but a non-exclusion proves only consistency, since millions of men share any blood group. Serology therefore moved to HLA, whose enormous polymorphism excluded the great majority of falsely accused men, and finally to DNA profiling: short tandem repeat analysis across standard loci yields a paternity probability above 99.9 per cent on non-exclusion, while a validated mismatch excludes absolutely. Indian law adds its own twist — section 112 of the Evidence Act (now section 116 of the Bharatiya Sakshya Adhiniyam) makes a child born during a valid marriage, or within 280 days of its dissolution, conclusive proof of legitimacy unless non-access is shown, and the Supreme Court has cautioned against routine DNA orders in matrimonial disputes.
What you must remember
- Exclusion doctrine: blood group exclusion is certain; inclusion is only probabilistic — the sentence on which every paternity answer is built.
- ABO worked examples: an O father cannot have an AB child; an AB parent cannot have an O child; a child lacking any allele present in both mother and putative father is excluded.
- HLA power: the HLA system's polymorphism excluded the great majority of falsely accused men (around ninety per cent) in the pre-DNA era — still a favourite exam line.
- DNA standard: short tandem repeat profiling at the standard battery of loci; non-exclusion reported as a probability exceeding 99.9 per cent, and validated mismatches exclude with certainty.
- Maternal trio rule: test mother, child and alleged father — subtract the mother's obligate alleles, then examine the paternal alleles for mismatches.
- Legal presumption: section 112 Evidence Act, renumbered as section 116 of the Bharatiya Sakshya Adhiniyam 2023 — birth within marriage or within 280 days of dissolution is conclusive proof of legitimacy, rebuttable classically by proof of non-access.
- Case-law discipline: Goutam Kundu (1993) — courts should not order blood tests routinely in matrimonial disputes; Nandlal Badwaik (2014) — DNA may be ordered when the interest of justice distinctly requires it.
- Maternity variants: switched newborns and abandoned infants are settled by the same technology in reverse — matching, not excluding.
Working through a disputed paternity case
A wife in a maintenance proceeding names a man as her child's father; he denies ever having access to her. The court, balancing legitimacy presumption against truth, orders DNA profiling of the trio. Conventional typing screens first: the child's ABO and Rh alleles are consistent with mother and putative father — no exclusion, but that proves little. STR profiling follows: at every locus the child's paternal alleles trace to the alleged father, and the combined paternity index computes above 99.99 per cent. The report is worded with discipline — "the alleged father cannot be excluded and is 99.99 per cent likely to be the biological father" — never "is the father," because statistics assign likelihood, courts assign fatherhood. A decisive mismatch would flip the report to outright exclusion, restated on a confirmatory retest. The court then weighs the DNA against the legitimacy presumption or the maintenance statute; the doctor's role ends at the laboratory door — science narrows, law decides.
Where the viva probes
The opener is nearly always the exclusion principle, best answered with a worked ABO example spoken aloud. The second probe is why DNA can claim 99.9-plus per cent when blood groups cannot — allele frequencies, independence of loci, and the multiplication of the paternity index across systems. The Indian law question follows: the strong answer explains the 280-day window, the non-access exception, and judicial reluctance to order tests branding a child illegitimate. A final trap: "can DNA prove paternity?" — the disciplined answer is that it can exclude absolutely and include with overwhelming probability, and the difference in wording is the difference between a defensible report and a cross-examined one.
Frequently asked questions
Can blood grouping prove paternity?
No — blood groups can only exclude an alleged father with certainty; non-exclusion shows mere consistency, since the same groups occur in millions of men.
Which blood group combinations exclude paternity?
An O-group father cannot have an AB child, an AB parent cannot have an O child, and any child allele absent from both parents excludes the putative father.
How accurate is DNA profiling in paternity?
Exclusion is absolute on validated mismatches; non-exclusion is reported as a probability exceeding 99.9 per cent across the standard STR loci.
What does the law presume about a child born in wedlock?
Under section 112 of the Evidence Act, now section 116 of the Bharatiya Sakshya Adhiniyam, birth during marriage or within 280 days of dissolution is conclusive proof of legitimacy, rebuttable classically by non-access.
When will Indian courts order DNA testing in paternity disputes?
Not routinely — per Goutam Kundu, only when a strong prima facie case exists and the interest of justice distinctly requires it, as refined in Nandlal Badwaik.