ESPM 150/290 Forensic Genetic Analysis 20 March, 2013 Guest Lecturer: Todd Osmun
Lewis, Keith, Owner has reference to this Academic Journal, PHwiki organized this Journal ESPM 150/290 Forensic Genetic Analysis 20 March, 2013 Guest Lecturer: Todd Osmundson, Ph.D. Postdoctoral Researcher, Garbelotto Lab The case of Colin Pitch as long as k Narborough, Leicestershire, Engl in addition to , 1983 in addition to 1987: 2 brutal rapes/murders of 15-year-old girls unsolved. Cases so closely matched that police strongly believed a single suspect committed both. 1984, Leicester University: Professor Alec Jeffreys develops techniques as long as DNA fingerprinting A 17-year-old suspect first denied involvement, but under extensive questioning admitted to the second but not the first murder Genetic comparison of crime scene in addition to suspects blood samples showed he was not responsible as long as either murder. Thus, Richard John Buckl in addition to was the first person exonerated of a crime by DNA evidence. The case of Colin Pitch as long as k Police subsequently took blood samples from every 13-30-year-old man in 3 local villages A local bakery owner overheard a conversation where one man bragged about paying someone else to provide a sample on his behalf, reported him to police, in addition to man was apprehended DNA evidence implicated the man, Colin Pitch as long as k, in the crimes – the first person to be convicted based on genetic fingerprinting
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How can we assess the relatedness of individuals Inheritance = Passing of genetic material (DNA) from parent to offspring Relatedness = proportion of genetic material shared between individuals I. A Brief Genetics Primer
Sources: (clockwise from upper left: http://www.healthinmotion.net/HIM/HTM/LS.html; http://www.alzheimers.org/rmedia/IMAGES/LOW/Dna-low.jpg; http://radiographics.rsna.org From Tissues to Cells to Genes DNA Structure DNA is the genetic in as long as mation-carrying molecule in a cell 4 building blocks (bases): Adenine, Cytosine, Guanine, in addition to Thymine A in addition to T bind together G in addition to C bind together 2 str in addition to s arranged in a double helix The sequence of a piece of DNA is the order of its bases, depicted as a string of letters (e.g., TGCATTACTACGTG) Because of the predictable pattern of complementary binding (A +T, G + C), if we determine the sequence of one str in addition to , we automatically know the sequence of the other str in addition to DNA is Arranged into Chromosomes http://www.uic.edu/classes/bios/bios100/lecturesf04am/realchromo.jpg
Our chromosomes come in pairs: one from our mother, one from our father. (a) Chromosomal composition found in most female human cells (46 chromosomes) (b) Chromosomal composition found in a human gamete (23 chromosomes) 1 2 3 4 5 6 7 XX 8 9 10 11 12 13 14 15 17 18 19 20 21 22 16 1 2 3 4 5 6 7 X 8 9 10 11 12 13 14 15 17 18 19 20 21 22 16 For reproduction, our gametes (egg, sperm) have to have half of the normal number of chromosomes (otherwise, our offspring would have 2X our number of chromosomes) (a) Chromosomal composition found in most female human cells (46 chromosomes) (b) Chromosomal composition found in a human gamete (23 chromosomes) 1 2 3 4 5 6 7 XX 8 9 10 11 12 13 14 15 17 18 19 20 21 22 16 1 2 3 4 5 6 7 X 8 9 10 11 12 13 14 15 17 18 19 20 21 22 16 Mitosis Cell division that creates genetically identical daughter cells Normal growth Asexual organisms
Meiosis Cell division that creates gametes with ½ the normal number of chromosomes Sexual organisms Animal Gametogenesis Fertilization Chromosomes from the 2 parents join during fertilization Paired chromosomes (one from each parent) are similar but not identical Different as long as ms of a gene are known as alleles www.center4fertility.com
Loci in addition to Alleles Locus (plural: loci): location of a gene on a chromosome (e.g., gene that controls flower color by encoding a protein involved in pigment synthesis) Allele: specific as long as m of a gene (producing purple flowers or not) II. Molecular Markers Molecular Markers Within sexually-reproducing species, individuals are related by heredity Offspring are genetically similar to parents, but differ genetically due to 3 phenomena: Meiotic segregation in addition to independent assortment: Gametes receive only one chromosome from each pair Crossing over during Meiosis I Combination of 2 parental gametes during fertilization results in new genetic combinations Additional genetic differences result due to mutation
Molecular Markers Sexual reproduction means that an allele that arises by mutation can be spread within the population. Sharing of DNA within a population (via mating) is known as gene flow Separated populations may experience limited or no gene flow. Migration of individuals between populations, followed by mating, allows gene flow between populations evolution.berkeley.edu Molecular Markers Sexual reproduction (interbreeding within a population) tends to homogenize (spread) the alleles present within a population. Conversely, when sexual reproduction is reduced or inhibited, different (sub)populations accumulate differences; can lead to speciation evolution.berkeley.edu Molecular Markers In asexually-reproducing organisms, new individuals are produced by mitosis (or similar mechanisms such as fission or budding) There as long as e, offspring are genetically identical to parent Genetic differences between individuals result due to mutation Would you expect sexual or asexual organisms to have higher population-level genetic diversity
Molecular Markers Because related individuals share genetic (DNA) similarities, we can examine DNA to infer many things about an organism, such as: What species does it belong to Origin in addition to movement: Where did it come from What are its patterns of migration What is its natural dispersal capacity Has it moved as a result of human activity Does it reproduce sexually or asexually Molecular Markers We can look at the DNA sequence directly ( as long as single genes up to the whole genome), or we can use proxy methods that examine genotype more indirectly. These genotype differences that we can examine are known as molecular markers. III. Major Types of Molecular Markers
DNA Sequences Sequence: The order of nucleotides in a particular region of DNA. Order matters, like letters in a word: RATS TARS ARTS STAR TRAS RTSA DNA Sequence Identification Example: querying the GenBank database to determine the identity or putative function of an unknown DNA sequence by comparing it to the sequence of known genes. DNA Barcoding Identification of species by sequencing an agreed-upon gene (cytochrome oxidase 1 as long as most animals; rDNA internal transcribed spacer as long as fungi) Assuming that each species differs in the sequence of this gene ( in addition to that the gene sequence is constant within a species), each species will have a unique genetic code, analogous to the supermarket UPC code.
Comparison of new DNA sequence to existing barcode database DNA Barcoding: Uses Identifying cryptic species (different species that cannot be distinguished just by looking at them) Matching different life stages (e.g., larvae in addition to adults) Identifying species when distinguishing characteristics are missing (e.g., plants lacking flowers; fungi lacking spores) DNA Barcoding: Uses Identifying species in processed products Sushi, caviar Teas Herbal medicines
Garbelotto (2008) Modes of introduction: 1. Direct introduction from native source 2. Short-term indirect 3. Long term indirect (routine) commons.wikimedia.org as long as estphytophthoras.org Garbelotto (2008) Phase II: Establishment Pathogen invades suitable host(s); population size begins to increase Symptoms on host are often the first clue that the disease is present; epidemics often first spotted in establishment (not introduction) phase Characteristics: Genetic bottlenecks Disequilibrium Strong genetic structuring Sexual vs. asexual reproductive modes Garbelotto (2008) Phase III: Invasion Spread of the exotic pathogen into new habitats in addition to host populations Potential as long as further genetic bottlenecks because of the loss of alleles by genetic drift in small new populations. 2 elements may be required as long as a successful invasion: population sizes need to increase in order to limit the effects of genetic drift, in addition to new genetic variability needs to arise, either through mutation, recombination, or interspecific gene flow.
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