Forensics: Using DNA to distinguish individuals Need: Rapid and reliable markers Sufficient numbers of polymorphic markers to be sure that no other person could be a match DNA amplification methods to obtain information from samples that are: very small have DNA degradation

Example of paternity test With this information, we can only exclude the accused from being a parent. With DNA technology, we have so many markers that the probability of mistaken identity becomes very small

Insertion-deletion polymorphism Variable number tandem repeats- Minisatellites ( bp repeats) Short tandem repeats- Microsatellites (1-3 bp repeats) Single nucleotide polymorphisms Different types of DNA markers

Insertion-deletion polymorphism Allele 1 Allele 2 Transposon, retrovirus, etc Point of reference Restriction site PCR primer Sobrino et al 2005 Forensics Sci. Int. 154:

VNTR Variable Nucleotide Repeats

Fig Microsatelites 1-3 bp repeats Polymerase pauses, replication continues out of register

Up to 100bp repeats

PCR can ease identification of polymorphic sequences.

Microsatellites or minisatellites can be detected by PCR Use PCR to amplify sequences starting with primers designed from single copy sequence that flanks repeats

Genetic variation in a sequence with a minisatellite used in DNA typing

SNP Single nucleotide polymorphisms The Human Genome Project has identified 300,000 SNPs common to human genomes Sometimes in restriction sites-RFLP Several new methods for detection

Sobrino et al 2005 Forensics Sci. Int. 154:

Fig

microarrays

Full genome sequencing New technologies will make it practical to analyze the full DNA sequence of any person for a few thousand dollars, perhaps by the end of 2008.

Thomas Jefferson paternity investigation

Was Jefferson the father of Sally Hemmings children? 1786: Sally accompanied Jefferson to Paris as companion for his daughter while Jefferson was ambassador to France 1789: Jefferson household returned to America Sally remained in the Jefferson household She bore 5 children. The oldest was Tom in 1790 and the youngest was Eston in In 1802 Jefferson was accused of fathering Tom. He denied the accusation and the investigation was eventually dropped. Jefferson’s daughter claimed that at least some of Sally’s children were fathered by one of her cousins on her mother’s side, the Carrs.

Tom was sold to the Woodson family and took the name Tom Woodson. Eston took the name Eston Hemmings Jefferson He moved to Madison Wisconsin where he was accepted as a member of white society.

Forster et al investigated the descendants of Tom and Eston and their prospective fathers DNA from the Carr family male descendants DNA from the male descendants of Jefferson’s Uncle, Field Jefferson DNA from Tom Woodson’s male descendants DNA from Eston Jefferson’s male descendants Y chromosome markers: No recombination Stable polymorphisms

Current members of the Jefferson and Carr families Founding father

Conclusions: Thomas Woodson was fathered by a Carr. President Jefferson did not lie when he denied being the father of Thomas Woodson. Eston was fathered by a Jefferson. Are we sure he was fathered by President Jefferson? When you have your Y chromosome DNA examined, you may come in for an unexpected surprise.