1. DNA in Forensic

By Dr. Tiana Milanda

www.themegallery.com Company Name

Introduction In the late 1800s, efforts to fight crime were given by

photography limitations : criminals found may ways to alter their appearance.

100 years ago, scientists discovered that the tiny arches and whorls in the skin of the fingertips could be to establish identity.

They need a huge collections of prints and clerks were responsible for examining each set of possible prints to find matches the process became less tedious and more realiable with a computer

Limitations : fingerprints can be wiped away and gloves can be worn to keep from leaving fingerprints behind.

In 1985, a new kind of “fingerprinting” : DNA fingerprint

DNA Structure DNA/polinucleotide is made

up of a series of monomers called nucleotides.

Each nucleotide has three parts : a nitrogenous base :

interchangable components a pentose sugar (5C)

deoxyribose in DNA ribose in RNA

a PO4 group

DNA Structure

2 types of nitrogen bases : Purines, double ring N base :

adenine (A) guanine (G)

Pyrimidines, single ring N base : cytosine (C) thymine (T) in DNA uracil (U) in RNA

DNA Structure Polinucleotide: backbone

the sugar of one nucleotide connect (C3) to the PO4 group (C5) of an adjacent nucleotide = phosphodiester bond

The bases N bases hang off the

sugar-phosphate backbone single nucleotide chain (C1)

Each strand of polinucleotide has polarity : 5’ end (PO4 end) 3’ end (OH end)

DNA structureThe two strands of a DNA molecule are joined by H bonds between complementary base pairs

in opposite strand purine :: pyrimidine A :: T

2 H bonds G :: C

3 H bonds

DNA structure Two strands of DNA are

considered antiparalel, because the polarity of each strand is reversed relative to each other a double helix

Major groove

Minor groove

turned right“B structure” DNA

5’

3’

3’

5’

Human DNA Packing In human cells, DNA are packing in nuclear

chromosome and cytoplasmic mitochondria chromosome

Nuclear chromosomes

In every human cell, 3.1 billion bp (base pair) of DNA (6 feet) fit into a nucleus

These DNA wrapped around proteins and organized into tightly coiled units called chromosomes

Nuclear chromosomes

female

male

• Human cells : somatic cells and gametes

• Each somatic cells have two sets of 23 linear chromosomes (diploid), 23 maternal chromosomes and 23 paternal chromosomes homologous pairs

Homologous chromosomes Paired chromosomes

both chromosomes of a pair carry genes control same inherited characters homologous = same information

diploid2n

homologouschromosomes

double strandedhomologous chromosomes

Nuclear chromosomes

female

male

• Chromosomes 1-22 autosomes, chromosomes 23 sex chromosomes, consisting of X and Y chromosome

• Autosomes contain genes that affects other body features unrelated to sex

• Sex chromosome contain genes that influence sex traits and the development of reproductive organs

Nuclear chromosomes

female

male

• Human males have an X and a Y chromosomes (XY) and females have a pair of X chromosomes (XX)

• A set genes found on the Y chromosomes, called SRY (sex-determining region) determine an embryo into a male or female

Nucleic Acids Res. 28(2), e8 (2000)

Y Chromosome Structure

~2.5 Mb on tips recombine with X (pseudoautosomal regions)

~60 Mb total DNA sequence (only chromosome 22 is smaller)p

q

heterochromatin

35-36 Mb euchromatin 9.5 Mb sequenced (27%)

AMEL

SRY

Genetic variation at multiple points along the Y chromosome is combined to form a Y haplotype for a sample

Genetic variation at multiple points along the Y chromosome is combined to form a Y haplotype for a sample

Nuclear chromosomes Each gametes (sperm or

ovum cells) contains 23 linear chromosomes (haploid)

A diploid fertilized egg (zygote) is formed each time a sperm and egg fuse

Its diploid set is passed on to newly formed somatic cells by mitosis

A process called meiosis produces gametes

Mitosis vs Meiosis

Mitosis vs Meiosis

Mitosis 1 division daughter cells

genetically identical to parent cell

produces 2 cells 2n → 2n produces cells for

growth & repair no crossing over

Meiosis 2 divisions daughter cells

genetically different from parent

produces 4 cells 2n → 1n produces gametes

crossing over

Genetic variation : in human Genetic variability in sexual reproduction

independent assortment homologous chromosomes in meiosis 1

crossing over between homologous chromosomes in prophase 1

random fertilization random ovum fertilized by a random sperm

metaphase1

Independent assortment Meiosis introduces genetic variation

gametes of offspring do not have same genes as gametes from parents

genetic recombination random assortment in humans produces 223

(8,388,608) different combinations

from Mom from Dadnew gametes

made by offspring

Crossing over During prophase 1

homologous pairs swappieces of chromosome

sister chromatids intertwinecrossing over

tetrad

synapsis

Random fertilization Any 2 parents will produce a zygote with

over 70 trillion (223 x 223) diploid combinations

Mitochondrial DNAMitochondria - The powerhouse of the cell.

The number of mitochondria varies greatly with the type of cell and stage of its development (ranging 200-1,000)

Mitochondria

Mitochondria have their own DNA

Mitochondrial DNA

Double Helix NuclearChromosomes

Mitochondrial DNA

Each mitochondrion contains two or three circular DNA

Coding and non coding sequences

Nuclear and mitochondrial chromosomes consist of two types of nucleotides

1. Those that make up the genes, called coding

sequences

2. Those whose function is largerly unknown, called non

coding regions The nucleotide in coding and non coding portion are

alike, they differ solely in whether or not they contribute to one or more of the individual’s trait (phenoptype)

Gene

A gene is a sequence of nucleotides (1,000-4,000 bp) for the synthesis of a specific polypeptide or a specific protein or a particular type of RNA.

By controlling the proteins produced by a cell, genes influences how cells, tissues and organs appear.These inherited appearances are called traits.

Nuclear : Non coding sequence

3’5’

3’

5’Gene 1 Gene 2

Intergenic DNA

3’5’

3’

5’Gene 1 Gene 2

Introns

Nucleus :

Eukaryotic genomes full of repeated DNA

Satellite DNA

Minisatellite DNA or

Variable Number of Tandem Repeats (VNTR)

Microsatellite DNA or

Short Tandem Repeats

Repeat Unit # Repeats

100 – 1000 bp

10 – 100 bp

2 – 6 bp

7 - 80

???

5 - >40

VNTR Rectangle blocks represent repeated DNA sequences at

a particular VNTR location Repeats are tandem – clustered together and oriented in

same direction Repeats can be removed or added leading to alleles with

different numbers of repeats.

Types of STRs

Dinucleotide, trinucleotide, tetranucleotide, pentanucleotide, hexanucleotide.

Complex repeats: repeat blocks varying in unit length and sequence

Compound repeats: two or more adjacent simple repeats.

Simple repeats: identical length and sequence.

Person 1 ..GCCAGCTAGCTAGCTAGCTAGCTAGCTTTCAT..1 2 3 4 5 6

Person 2 ..GCCAGCTAGCTAGCTAGCTAGCTTTCAT..

Person 3 ..GCCAGCTAGCTAGCTAGCTAGCTAGCTAGCTT..

1 2 3 4 5

1 2 3 4 5 6 7

On average, occur every 10,000 nucleotides.

Short Tandem Repeats

Locus or Loci:Refers to the location on the chromosome.

Allele:Refers to the type of DNA.

LOCUS AND ALLELE

Each person has 2 alleles at each locus.

D5S818

2 alleles per locus

Short Tandem Repeats

Person 1..GCCAGCTAGCTAGCTAGCTTTCAT..1 2 3 4

..GCCAGCTAGCTAGCTAGCTAGCTAGCTTTCAT..1 2 3 4 5 6

Person 2..GCCAGCTAGCTAGCTAGCTAGCTAGCTTTCAT..1 2 3 4 5 6

..GCCAGCTAGCTAGCTAGCTAGCTAGCTAGCTTTCAT..1 2 3 4 5 6 7

Person 3..GCCAGCTAGCTAGCTAGCTAGCTTTCAT..1 2 3 4 5

..GCCAGCTAGCTAGCTAGCTAGCTTTCAT..1 2 3 4 5

Homozygote = both alleles are the same length

Heterozygote = alleles differ and can be resolved from one another

Nuclear : Non coding sequence

3’5’

3’

5’Gene 1 Gene 2

Intergenic DNA

3’5’

3’

5’Gene 1 Gene 2

Introns

Loci Nomenclature

• Introns: STR name based on gene.

TH01 - located in the 1st intron (01) of gene for tyrosine hydroxylase

• Intergenic DNA: based on chromosome

D5S818

D = DNA

5 = chromosome 5

S = single copy in genome

818 = 818th locus

Coding and non coding sequences In a mitochondrial chromosome, the coding and non

coding areas are entire separate. Non coding portion being located in a region reffered as the control region (also called displacement loop or D-loop)

The control region contains 1,100 bp and is devided into 2 distinct sections, hypervarible 1 (HV1) and hypervarible 2 (HV2)

Summary

Two aspects of DNA : The uniform nature of DNA in a single individual

every cell in a body shares the same DNA The genetic variability between individual The

chemical structure of DNA is the same, but the order of the base pairs differs

The unique signature found in each person’s genetic makeup DNA fingerprint