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Paternity Testing

Paternity Testing. Biology Alliance May 13. A pair of homologous chromosomes , (one from mom, one from dad). Humans have 23 pairs of homologous chromosomes. Gene unit of DNA information about a trait passed from parents to offspring specific location on a chromosome.

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Paternity Testing

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  1. Paternity Testing Biology Alliance May 13

  2. A pair of homologous chromosomes, (one from mom, one from dad) Humans have 23 pairs of homologous chromosomes • Gene • unit of DNA information about a trait • passed from parents to offspring • specific location on a chromosome Alleles – different versions of a gene Human Chromosomes Fig. 8-1, p.113

  3. Polymerase Chain Reaction (PCR) • Developed in 1983 by Kary Mullis • Awarded Nobel Prize in 1993

  4. PCR Basics • Isolate and mass produce a particular DNA fragment • Template DNA • Polymerase – enzyme that replicates DNA, matches complementary bases • Primers –10-30 base pairs long, complementary to ends of fragment

  5. PCR Basics • Isolate and mass produce a particular DNA fragment • Denature • Anneal • Extend

  6. Short Tandem Repeats • Short regions of DNA that differ substantially among people • TCAT • Each person carries a unique combination of repeats

  7. (a) DNA and dye are loaded in a well on a gel, and an electric field is placed across the gel. DNA samples from PCR Well Gel Direction of electric field Electrode (b) DNA fragments move through the gel, shorter fragments faster than longer fragments.

  8. Applications? • Implicating a crime suspect, acquitting the wrongly convicted • Paternity • Identifying the deceased

  9. Obtaining DNA • Any biological material • Body tissues • Body fluids • Hair follicles • Dried material

  10. Power of Discrimination • Ability to discriminate between different individuals • The larger the number of loci used, the more powerful the ability to discriminate

  11. CODIS • COmbined DNA Index System • database of DNA obtained from crime scenes and convicted violent offenders • 13 loci

  12. Alleles

  13. Paternity Index 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 D8 hypothetical example: 13 is obligate allele, frequency of 9 = 0.308 PI = 0.5/0.308 = 1.62

  14. Paternity Index

  15. Combined Paternity Index (CPI) • All PI multiplied by each other 27,746

  16. Probability of Paternity CPI CPI + (1-prior probability) 27,746 27,746 + (1-0.5) x 100 x 100 = 99.998%

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