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Paternity Indices. Ronald S. Ostrowski, Ph.D. Department of Biology UNC-Charlotte 704-687-4057 email: rsostrow@email.uncc.edu. Forensic Inquiries:. Molecular Genetics Population Genetics. 3 billion base pairs total STR loci range from 114-142 to 281-317 base pairs.

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Paternity Indices

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Paternity Indices

Ronald S. Ostrowski, Ph.D.

Department of Biology

UNC-Charlotte

704-687-4057

email: rsostrow@email.uncc.edu


Forensic Inquiries:

  • Molecular Genetics

  • Population Genetics


  • 3 billion base pairs total

  • STR loci range from

  • 114-142 to 281-317 base pairs


STRs come in different sizes within a locus

(alleles – alternate forms)


  • 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


Homozygous

Heterozygous

Hypothetical D5 Gel Results:

LadderMom Child AF1 AF2 AF3

12, 13

9, 12

13, 14

12, 12

9, 12

14

7


NCSBI STR POPULATION DATA BASE

BLACKS


BLACKS


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


99.99%

27,237 to 1


Obligate

Allele

13

27

16

14

15

21

12

11

8

NA


NCSBI STR POPULATION DATA BASE

BLACKS


BLACKS


Combined Paternity Index (CPI)

Locus Allele Frequency PI

D8130.3080.5/0.308 =

D21270.0410.5/0.041 =

D18160.1250.5/0.125 =

D3140.1390.5/0.139 =

vWA150.2190.5/0.219 =

FGA210.1761.0/0.176 =

D5120.3580.5/0.358 =

D13110.2740.5/0.274 =

D780.1730.5/0.173 =

1.62

12.2

4.0

3.6

2.28

5.68

1.4

1.82

2.9


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


Probability of Paternity (POP):

(Bayes’ Theorem)

CPI

CPI + (1-prior probability) x 100

27,234

27,234 + (1-0.5) x 100 =

99.99%


Overview:

  • Loci/Alleles

  • PCR/Gel Electrophoresis

  • Obligate Alleles

  • Paternity Index (PI)

  • Combined Paternity Index (CPI)

  • Probability of Paternity (POP)

Discussion?


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