Paternity Testing Biology Alliance May 13
Feb 12, 2016
Paternity Testing
Biology AllianceMay 13
A pair of homologous chromosomes, (one from mom, one from dad)
Gene• unit of DNA information about a trait• passed from parents to offspring• specific location on a chromosome
Fig. 8-1, p.113
Alleles – different versions of a gene
Human Chromosomes
Humans have 23 pairs of homologous chromosomes
Polymerase Chain Reaction (PCR)
• Developed in 1983 by Kary Mullis• Awarded Nobel Prize in 1993
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
PCR Basics
• Isolate and mass produce a particular DNA fragment– Denature– Anneal– Extend
Short Tandem Repeats
• Short regions of DNA that differ substantially among people– TCAT
• Each person carries a unique combination of repeats
(a) DNA and dye are loaded in a well on a gel, and anelectric field is placed across the gel.
(b) DNA fragments move through the gel, shorter fragments fasterthan longer fragments.
Electrode
GelWellDNA samples from PCR
Direction ofelectric field
Applications?
• Implicating a crime suspect, acquitting the wrongly convicted
• Paternity• Identifying the deceased
Obtaining DNA
• Any biological material– Body tissues– Body fluids– Hair follicles– Dried material
Power of Discrimination
• Ability to discriminate between different individuals
• The larger the number of loci used, the more powerful the ability to discriminate
CODIS
• COmbined DNA Index System• database of DNA obtained from crime scenes
and convicted violent offenders• 13 loci
Alleles
Paternity IndexLikelihood ratio: X/Y
X = chance that the AF could transmit the obligate alleleY = chance that some other man of the same race could have transmitted the allele
X = 1 if father is homozygousX = 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
Paternity Index
Combined Paternity Index (CPI)
• All PI multiplied by each other
27,746
Probability of Paternity
CPI CPI + (1-prior probability)
27,746 27,746 + (1-0.5)
x 100
x 100 = 99.998%