Post on 02-Jan-2016
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Why test DNA?
• Match suspect/victim/evidence
• Convicted felon databases
• Missing persons investigations
• Maternity/paternity – kidnapping
• Military – remains from war
• Mass disasters – ID victims
DNA FingerprintingDNA Fingerprinting
Sources of DNA at a Crime Scene
Blood (WBC’s)
Semen – sexual offences, (sperm head)
Saliva – stamps, envelopes, straw, glass, gum
Urine – if blood cells were shed
Hair - if follicle, shaft mtDNA
Bone Marrow – retains DNA for years
Tissue – flesh/organs decompose quickly, not good
What are the 2 types of DNA?
• 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
Which type is better for forensic testing?
DNA in the Cell
chromosome
cell nucleus
Double stranded DNA molecule
Individual nucleotides
Each nucleotide contains:
Nitrogenous Base
Sugar (deoxyribose)
Phosphate Group
4 different bases make up the steps of the ladder
A Adenine T Thymine G Guanine C Cytosine
Base Pairing Rules
Sugar-Phosphate backbone
G-C A-T
Each rung on the ladder is called a
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
base-pair
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
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%
Nuclear DNA is in every nucleated cell of the body.
• Every body cell has 46 chromosomes.
• Every sex cell (egg/sperm) has 23 chromosomes.
Human KaryotypeGenome: all genetic material in a nucleus.
Humans:
22 pairs of autosomes
1 pair of sex chromosomes
X & Y
Organization of the Human GenomeLocus – Specific region (address on a chromosome)
GeneGene – region that – region that encodes for a encodes for a protein or a traitprotein or a trait
Marker LocusMarker Locus – – non-coding regionnon-coding region
Eye colorEye color
DimplesDimples
FrecklesFreckles
Blood typeBlood type
Non-coding Non-coding “junk DNA”“junk DNA”
MOM DAD
Organization of the Human GenomeEvery gene or locus marker can have alternate forms
called alleles
Blue eyesBlue eyes
DimplesDimples
No FrecklesNo Freckles
Type IType IAA
Non-coding Non-coding “junk DNA”“junk DNA”
For every gene/locus in your DNA you have… 2 alleles.
Homozygous (same)
Heterozygous (different)
MOM DAD
Brown eyesBrown eyes
No dimplesNo dimples
FrecklesFreckles
Type IType IBB
How do these alleles
differ?
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
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
GACA GACA GACA GACA GACAPolymorphism – an alternate version
STR’s Short Tandem Repeats (smaller segments with fewer repeats)
CGAA CGAA CGAA CGAA CGAA CGAA CGAA CGAA CGAA CGAA CGAA
VNTR’s Variable Number Tandom Repeats (larger segments with many repeats)
GGACTAATATCTATTCCCTAATATGACTAA
AATATTTCGGACTAGATATCTTTCGGACTTA
TCTATTCGGGAGCCGCTACCCGTG…
…X 1000
A locus marker that includes a tandem repeat sequence can have many different alleles in a population. Ex:
Allele 1: (6 repeats)
GAACT ATTA ATTA ATTA ATTA ATTA ATTA CGTGCAGGCT
Allele 2: (5 repeats)
GAACT ATTA ATTA ATTA ATTA ATTA CGTGCAGGCT
Allele 3: (7 repeats)
GAACT ATTA ATTA ATTA ATTA ATTA ATTA ATTA GTGCAGGCT
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 GG 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 GG 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
This Allelic variation is the This Allelic variation is the basis for forensic DNA testing.basis for forensic DNA testing.
• Many polymorphic loci in human genome.Many polymorphic loci in human genome.
• Each locus has many forms (alleles).Each locus has many forms (alleles).
How do we process and visualize How do we process and visualize the DNA for comparison?the DNA for comparison?
2 types of DNA Fingerprinting2 types of DNA Fingerprinting• RFLPRFLP ( (olderolder ) involves STR’s & VNTR’s ) involves STR’s & VNTR’s• PCRPCR ( (newer) newer) involves STR’sinvolves STR’s