DNA is located in cells which are the building blocks of the human body
Two Types of cells: Sex Cells Somatic Cells Where are these cell types located in a
human being? How are they different from one another?
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DNA can be found in any nucleated cell All nucleated cells in a body contain the
same DNA Rare mutations can lead to slight differences
Many types of crime scene evidence can contain nucleated cells and thus be a source of DNA for typing
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Blood
Very common at violent crime scenes Consists of erythrocytes (red blood
cells), leucocytes (white blood cells), and platelets
Nuclear DNA obtained from leucocytes; erythrocytes and platelets lack nuclei and DNA
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Hair Consists of root and shaft Medulla Cortex Cuticle Grows at approximately 0.3mm per day Anagen phase- growing phase Catagen phase- follicle becomes inactive Telogen phase- growth cycle ends
Forensic Biology by Richard Li 9
Hair The shaft contains very little nuclear
DNA but lots of mitochondrial DNA More mtDNA genomes per cell than nuclear
genomes The root contains enough nuclear DNA
for standard DNA profiling Rooted hairs are less common at crime
scenes than unrooted (shed) ones People shed more than 50 hair shafts per day Rooted hairs must be pulled out by force
Forensic Biology by Richard Li 12
Hair as a source of DNA evidence PCR allowed more productive analysis of
hair Formerly just analyzed morphology and
comparisons mtDNA can be isolated from roots and shafts Nuclear DNA analysis or hair is preferred ▪ Plucked hair with roots▪ Naturally shed hairs contain little nuclear DNA▪ Most hairs at crime scenes are naturally shed
Forensic Biology by Richard Li 13
Bone Compact vs. Spongy▪ Spongy degrades more quickly after death than
compact Osteocytes▪ Most abundant cells in bone but cannot divide▪ Contains most of the DNA in compact bone
Osteoblasts▪ Produce new bone matrix
Osteoclasts▪ Dissolve and recycle the bone matrix
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Bone Rate of degradation of human remains
varies greatly with environmental conditions
Soft tissue is lost Bones are more stable Mass Fatalities-identify victims Sanding- used to reduce potential of
comingled remains, adhering inhibitors, and bacterial contamination
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Teeth
Deciduous /Primary teeth (20) vs. Secondary (32)
Dentin- Does not contain cells Pulp Cavity▪ Contains lots of cells and DNA
Root▪ Contains root canal with cells and DNA
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