Mitochondrial analysis in Forensic Scienses

Transcription

1 Mitochondrial analysis in Forensic Scienses 2011

2 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)

3 Human Genome Organization HUMAN GENOME From: Dr Finbarr Hayes lec Coding DNA Nuclear genome 3000 Mb genes 30% 70% Genes and generelated sequences Noncoding DNA Extragenic DNA Unique or moderately repetitive 10% 90% Two rrna genes Mitochondrial genome 16.6 kb 37 genes Unique or low copy number 22 trna genes 80% 20% 13 polypeptideencoding genes Moderate to highly repetitive Pseudogenes Gene fragments Introns, untranslated sequences, etc. Tandemly repeated or clustered repeats Interspersed repeats

4 Small but well characterized regions within the genome that vary between individuals forensic genetics: identification

5 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

6 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

7 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

8 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

9 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

10 H strand enriched in G L strand enriched in C

11

12 The human nuclear and mitochondrial genomes Size No. of different DNA molecules Total no. of DNA molecules per cell Associated protein No. of genes Gene density Nuclear Genome 3200 Mb 23 (in XX cells) or 24 (in XY cells); all linear 46 in diploid cells, but varies according to ploidy Several classes of histone & nonhistone protein ~ ~ ~ 1/100 kb Mitochondrial Genome 16.6 kb One circular DNA molecule Often several thousands (but variable Largely free of protein 37 1/0.45 kb

13 Table continued.. Repetitive DNA Over 50% of genome Very little Transcription Introns The great bulk of genes are transcribed individually Found in most genes Co-transcription of multiple genes from both the heavy and light strands Absent % of coding DNA ~ 1.5% ~ 93% Codon usage Slightly different see slide Recombination Inheritance At least once for each pair of homologs at meiosis Mendelian for sequence on X and autosomes; paternal for sequence on Y No evidence for this occurring naturally Exclusively maternal

14 Organization of the human genome Limited autonomy of mt genomes mt encoded nuclear NADH dehydrog 7 subunits >41 subunits Succinate CoQ red 0 subunits 4 subunits Cytochrome b-c1 comp 1 subunit 10 subunits Cytochrome C oxidase 3 subunits 10 subunits ATP synthase complex 2 subunits 14 subunits trna components 22 trnas none rrna components 2 components none Ribosomal proteins none ~80 Other mt proteins none mtdna pol, RNA pol etc.

15

16 The nuclear and Mitochondrial genetic codes are similar but not identical

17 The limited autonomy of the mitochondrial genome Mitochondrial component Encoded by Mitochondrial genome Encoded by nuclear genome Components of oxidative phosphorylation system Components of protein synthesis apparatus 13 subunits subunits approx 80

18 Number of Mitochondria per cell Most somatic cells ,000 Lymphocyte 1000 Oocytes 100,000 Sperm few hundred No mitochondria in red cells and some terminally differentiated skin cells

19 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

20 Maternal Inheritance of mtdna

21 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