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Why test DNA?

Why test DNA?. DNA Fingerprinting. Match suspect/victim/evidence Convicted felon databases Missing persons investigations Maternity/paternity – kidnapping Military – remains from war Mass disasters – ID victims. Sources of DNA at a Crime Scene. Semen – sexual offences, (sperm head).

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Why test DNA?

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  1. Why test DNA? DNA Fingerprinting • Match suspect/victim/evidence • Convicted felon databases • Missing persons investigations • Maternity/paternity – kidnapping • Military – remains from war • Mass disasters – ID victims

  2. Sources of DNA at a Crime Scene Semen – sexual offences, (sperm head) Blood (WBC’s) Bone Marrow – retains DNA for years Hair - if follicle, shaft mtDNA Tissue – flesh/organs decompose quickly, not good Saliva – stamps, envelopes, straw, glass, gum Urine – if blood cells were shed

  3. Nuclear DNA $100-200 per test 24-36 hours for results Shows genetic lineage from both parents Only 1 nucleus per cell Mitochondrial DNA(mtDNA) $1000 per test 1-6 weeks for results Shows only maternal lineage Many mitochondria/cell hours What are the 2 types of DNA? Which type is better for forensic testing?

  4. chromosome cell nucleus Double stranded DNA molecule Individual nucleotides DNA in the Cell

  5. Each nucleotide contains: Nitrogenous Base Phosphate Group Sugar (deoxyribose)

  6. 4 different bases make up the steps of the ladder A Adenine T Thymine G Guanine C Cytosine

  7. Base Pairing Rules G-C A-T Sugar-Phosphate backbone

  8. Each rung on the ladder is called a base-pair 1 base pair (bp) 2 base pair (bp) 3 base pair (bp) How many base-pairs are there in the human genome? ( in 1 nucleus / 46 chromosomes) approximately 3 billion

  9. A C G G T A A G C A T A G C C G T G A G T T T A C C A G

  10. The Genetic Code A series of G’s A’s C’s & T’s DNA Fingerprinting: identifies people by their unique genetic code How much of your DNA is identical to everyone else? 99.4%

  11. Nuclear DNA is in every nucleated cell of the body. • Every body cell has 46 chromosomes. • Every sex cell (egg/sperm) has 23 chromosomes.

  12. Human Karyotype Genome: all genetic material in a nucleus. Humans: 22 pairs of autosomes 1 pair of sex chromosomes X & Y

  13. Organization of the Human Genome • Locus – Specific region (address on a chromosome) • Gene – region that encodes for a protein or a trait • Marker Locus – non-coding region Eye color Dimples Freckles Blood type Non-coding “junk DNA” MOM DAD

  14. Organization of the Human Genome Every gene or locus marker can have alternate forms called alleles Brown eyes Blue eyes Dimples No dimples • For every gene/locus in your DNA you have… 2 alleles. • Homozygous • (same) • Heterozygous (different) Freckles No Freckles Type IB Type IA Non-coding “junk DNA” How do these alleles differ? MOM DAD

  15. DNA (Marker Loci) “junk” • How much? • 95% of genome • Function? • Somewhat unknown • Controls gene expression • Do we all have the same marker loci ? • Yes, but slightly different alleles • Ex: Contains different amounts of tandem repeated segments • GACAGACAGACAGACAGACA Polymorphism – an alternate version DNA (Genes) How much? 5% of genome 30,000 genes Function? Codes for traits & proteins Do we all have the same genes ? Yes, but slightly different alleles Ex: brown, blue, green eyes

  16. STR’s Short Tandem Repeats • (smaller segments with fewer repeats) CGAACGAACGAACGAACGAACGAA CGAA CGAA CGAACGAACGAA VNTR’s Variable Number Tandom Repeats • (larger segments with many repeats) GGACTAATATCTATTCCCTAATATGACTAA AATATTTCGGACTAGATATCTTTCGGACTTA TCTATTCGGGAGCCGCTACCCGTG… …X 1000

  17. A locus marker that includes a tandem repeat sequence can have many different alleles in a population. Ex: Allele 1: (6 repeats) GAACT ATTAATTAATTAATTAATTAATTA CGTGCAGGCT Allele 2: (5 repeats) GAACT ATTAATTAATTAATTAATTA CGTGCAGGCT Allele 3: (7 repeats) GAACT ATTAATTAATTAATTAATTAATTAATTA GTGCAGGCT

  18. C G C C A T G C A T G T G A G C G C G T A C G C C A C T G C A T G C C G G C G G T A C G T A C A C T C G C G C A T G C G G T G A C G T A C G G C C G C C A T G C A T G T G A G C G C G T A C C T C A C T G C A T G C C G G C G G T A C G T A C A C T C G C G C A T G G A G T G A C G T A C G G C Locus # 1 Locus # 2 A T C A G C A T T G A T T G A T T G A T T G A C C C A T A T G T G A G C G C G T A C C T C A C T G C G T A G T C G T A A C T A A C T A A C T A A C T G G G T A T A C A C T C G C G C A T G G A G T G A C C T G T T G A T C A G C A T T G A T T G A T T G A C C C A T A T G T G A G C G C G T A C C T C A C T G C G C A A C T A G T C G T A A C T A A C T A A C T G G G T A T A C A C T C G C G C A T G G A G T G A C C T

  19. This Allelic variation is the basis for forensic DNA testing. • Many polymorphic loci in human genome. • Each locus has many forms (alleles). How do we process and visualize the DNA for comparison? 2 types of DNA Fingerprinting • RFLP (older ) involves STR’s & VNTR’s • PCR (newer) involves STR’s

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