1. dna in forensic
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Transcript of 1. dna in forensic
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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 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.
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