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Paternity Indices

Paternity Indices

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Paternity Indices

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  1. Paternity Indices Ronald S. Ostrowski, Ph.D. Department of Biology UNC-Charlotte 704-687-4057 email: rsostrow@email.uncc.edu

  2. Forensic Inquiries: • Molecular Genetics • Population Genetics

  3. 3 billion base pairs total • STR loci range from • 114-142 to 281-317 base pairs

  4. STRs come in different sizes within a locus (alleles – alternate forms)

  5. Locus D5: • Alleles range from • 135-171 base pairs • Each allele is an increase • of 4 base pairs • Locus FGA: • Alleles range from • 219-267 base pairs • Each allele is an increase • of 4 base pairs

  6. Homozygous Heterozygous Hypothetical D5 Gel Results: Ladder Mom Child AF1 AF2 AF3 12, 13 9, 12 13, 14 12, 12 9, 12 14 7

  7. NCSBI STR POPULATION DATA BASE BLACKS

  8. BLACKS

  9. Paternity Index (PI) Likelihood ratio: X/Y X = chance that the AF could transmit the obligate allele Y = chance that some other man of the same race could have transmitted the allele X = 1 if father is homozygous X = 0.5 if father is heterozygous D5 hypothetical example: 9 was obligate allele, frequency of 9 = 0.017 PI = 0.5/0.017 = 29.4

  10. 99.99% 27,237 to 1

  11. Obligate Allele 13 27 16 14 15 21 12 11 8 NA

  12. NCSBI STR POPULATION DATA BASE BLACKS

  13. BLACKS

  14. Combined Paternity Index (CPI) Locus Allele Frequency PI D8 13 0.308 0.5/0.308 = D21 27 0.041 0.5/0.041 = D18 16 0.125 0.5/0.125 = D3 14 0.139 0.5/0.139 = vWA 15 0.219 0.5/0.219 = FGA 21 0.176 1.0/0.176 = D5 12 0.358 0.5/0.358 = D13 11 0.274 0.5/0.274 = D7 8 0.173 0.5/0.173 = 1.62 12.2 4.0 3.6 2.28 5.68 1.4 1.82 2.9

  15. CPI Calculation: 1.62 x 12.2 x 4.0 x 3.6 x 2.28 x 5.68 x 1.4 x 1.82 x 2.9= 27,234

  16. Probability of Paternity (POP): (Bayes’ Theorem) CPI CPI + (1-prior probability) x 100 27,234 27,234 + (1-0.5) x 100 = 99.99%

  17. Overview: • Loci/Alleles • PCR/Gel Electrophoresis • Obligate Alleles • Paternity Index (PI) • Combined Paternity Index (CPI) • Probability of Paternity (POP) Discussion?