Download Mitochondrial analysis in Forensic Scienses

Mitochondrial analysis in
Forensic Scienses
2011
Classification of human genome
• Genome
– 3.2 Gb
• Genic and related (25 %)
– Coding and regulatory (1.5 %)
– Non-coding (23.5% - introns, pseudogenes)
• Extragenic DNA (75%)
– Unique/low copy: 21%
– Repetitive DNA: 54%
• Tandem repeats (9%: satellites, micro-, mini-)
• Interspersed repeats (SINE, LINE, LTR, DNA transposons)
Human Genome Organization
From: Dr Finbarr Hayes lec
HUMAN GENOME
Nuclear genome
3000 Mb
65-80000 genes
30%
Genes and generelated sequences
Mitochondrial genome
16.6 kb
37 genes
70%
Extragenic
DNA
Two rRNA
genes
Unique or moderately repetitive
10%
90%
Coding
DNA
Pseudogenes
Noncoding
DNA
Gene
fragments
Introns,
untranslated
sequences, etc.
22 tRNA
genes
13 polypeptideencoding genes
80%
20%
Unique or
low copy
number
Moderate to
highly
repetitive
Tandemly
repeated
or clustered
repeats
Interspersed
repeats
Small but well characterized regions within the genome that vary between
individuals – forensic genetics: identification
DNA loci used in forensic genetics
• Highly polimorphic (vary widely between
individuals)
• Easy to characterize
• Give profiles easy to interpret and
compare between laboratories
• No under any selective pressure
• Have a low mutational rate
Types of biological material
• Scenes of Crime
–
–
–
–
Blood
Semen
Hair
Epithelial cells: saliva, dandruff, clothing, cigarette
butts, drinking vessels/food, urine, vomit, faeces,
touch DNA, debris from fingernails, postage stamps
• Reference Samples
– Blood
– Buccal swabs
– Pulled hairs
People of the State of California vs
OJ Simpson
• The Case
– 12 June 1994 Nicole Brown Simpson and Ronald
Goldman
• The Laboratories
– LA Police Department DNA Lab.,CA Department of
Justice DNA Lab., Cellmark Diagnostics (private,
Maryland)
– RFLP and PCR markers, but no STRs
– 61 items of evidence, 108 samples
• The Defence
– Evidence collection and preservation
– Contamination with OJS’s blood as reference sample
What is a Mitochondrion?
• A cellular organelle probably of endosymbiotic
origin that resides in the cytosol of most
nucleated (eurkaryotic) cells.
• This organelle produces energy by oxidising
organic acids and fats with oxygen by the
process of oxidative phosphorylation and
generates oxygen radicals (reactive oxygen
species ROS )as a toxic by-product
Mitochondrial Genetics
• Each cell contains many mitochondria,
each of which contains multiple copies
of 16.5-k-b circular DNA molecule
• The mitochondrial genome is subject to
a number of peculiarities of inheritance
H strand
enriched in G
L strand
enriched in C
The human nuclear and mitochondrial genomes
Nuclear Genome
Mitochondrial Genome
Size
3200 Mb
16.6 kb
No. of different DNA
molecules
23 (in XX cells) or 24
(in XY cells); all linear
One circular DNA
molecule
Total no. of DNA
molecules per cell
46 in diploid cells, but
varies according to
ploidy
Often several
thousands (but variable
Associated protein
Several classes of
histone & nonhistone
protein
Largely free of protein
No. of genes
~ 30 000 ~35-000
37
Gene density
~ 1/100 kb
1/0.45 kb
Table continued……..
Repetitive DNA
Over 50% of genome
Very little
Transcription
The great bulk of genes are Co-transcription of
transcribed individually
multiple genes from both
the heavy and light strands
Introns
Found in most genes
Absent
% of coding DNA
~ 1.5%
~ 93%
Codon usage
Slightly different see slide
Recombination
At least once for each pair
of homologs at meiosis
No evidence for this
occurring naturally
Inheritance
Mendelian for sequence on
X and autosomes; paternal
for sequence on Y
Exclusively maternal
Organization of the human genome
Limited autonomy of mt genomes
NADH dehydrog
Succinate CoQ red
Cytochrome b-c1 comp
Cytochrome C oxidase
ATP synthase complex
tRNA components
rRNA components
Ribosomal proteins
Other mt proteins
mt encoded
nuclear
7 subunits
0 subunits
1 subunit
3 subunits
2 subunits
22 tRNAs
2 components
none
none
>41 subunits
4 subunits
10 subunits
10 subunits
14 subunits
none
none
~80
mtDNA pol, RNA pol
etc.
The nuclear and Mitochondrial genetic
codes are similar but not identical
The limited autonomy of the mitochondrial
genome
Mitochondrial
component
Encoded by
Encoded by nuclear
Mitochondrial genome genome
Components of
oxidative
phosphorylation
system
13 subunits
80 subunits
Components of
protein synthesis
apparatus
24
approx 80
Number of Mitochondria per cell
•
•
•
•
Most somatic cells
Lymphocyte
Oocytes
Sperm
100-10,000
1000
100,000
few hundred
• No mitochondria in red cells and some terminally
differentiated skin cells
Maternal Inheritance of mtDNA
• during fertilization, the sperm only
contributes its nucleus (23 chromosomes)
• mitochondria of the sperm cell are located
at the mitochondrial sheath which is
destroyed upon fertilization
• the only available mitochondria (mtDNA) is
that of the mother's; this is why mtDNA is
of maternal origin
Maternal Inheritance of mtDNA
Key Facts
• mtDNA of siblings will match each others and
that of their mother
• mtDNA is found as a single, circular
chromosome in the cell
• mitochondrion may contain multiple copies of
mtDNA
• a human cell may contain hundreds or
thousands of mitochondria
• mtDNA may be useful when nuclear DNA is
limited because of its abundance