Chapter 2: Sources of DNA Evidence

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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Nucleated leukocyte surrounded by enucleated erythrocytes

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

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A hair follicle

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Cross section of a hair shaft

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

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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

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Hair morphology: Differences in human hair color

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Hair morphology: Absence (above) or presence (below) or medulla

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Hair morphology: Distinct cuticle layering patterns

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Pulled dreadlocks recovered from a crime scene

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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Anatomy of a bone

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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An adult human tooth

In addition to DNA analysis, teeth can be used to:

Identity a person▪ Characteristics of teeth▪ Alignment▪ Overall structure▪ X-rays

Compare suspect’s with bite marks on victim▪ What else might be present on a bite mark that

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