Why test DNA?

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