What is trace evidence? How does it help the case?
- Small pieces of physical evidence transferred during a crime
- Usually cannot positively i.d. a suspect on its own... But rather narrows down a group of suspects
Is hair individual or class evidence? How many hair fibers are there on a normal human scalp?
- Class evidence (unless root is present)
- 100 to 150 thousand hair fibers
What does it mean to have hair that is... Thick? Thin? Course? Fine?
Thick: High number of hair strands
Thin: Low number of hair strands
Course: The strand itself is thick
Fine: The strand itself is thin
What organ does each hair fiber root sit in? Why is there a small amount of blood?
- The organ is called a follicle... The organ is under the skin
- The "divot" is filled with blood, so if hair is pulled out of the head slowly, there will be a small amount of blood along with some cells
How fast does hair grow? Why does it differ from person to person?
- The average rate is 0.5 inches each month
- Growth rate is related to age, diet, etc.
What is human hair mainly made of? What protein is in hair? What are the three basic parts of hair?
- Composed of mainly amino acids that link to make protein
- The protein is called Keratin
- The three parts: Cuticle, Medulla, and Cortex
What is the cuticle? What is its job? What way do the scales point?
- The cuticle is a translucent outer layer
- Consists of scales that protect the strand
- The cuticle scales always point from root to tip
What are the three basic scale structures that make up the cuticle?
- Coronal (crown-like)
- Spinous (Petal-like)
- Imbricate (flattened)
What species normally have coronal cuticles?
Commonly found in small rodents and bats... Rarely in human hairs... Certain types of cats can also have this.... Cats with rougher fur
What species normally have spinous cuticles?
Found in mink hairs, seal hairs, cats, and some other animals. The fur is usually very soft. People usually make fur coats and scarves out of these.
What species normally have imbricate scales?
Found in human hairs and many animal hairs
What is the cortex? Why is it important? What do these cells contain?
- Cortical cells constitute the bulk of human hair
- These cells contain the pigment granules that give hair its color
What gives hair its color? How do the pigments in human hair differ from the pigments in animal hair?
- Melanin gives hair its color (like in skin)
- Humans generally have consistent pigment
- Animals may have different colored pigment (called bonding)... Ex: Foxes have red to black on a single strand
What is the medulla? What is its appearance in human hair? What is its appearance in animal hair?
- Medulla is a central core of cells that MAY be present in human hair
- The medulla is generally amorphous (not a specific shape) in appearance
- In animal hair, the medulla is most always present and well defined
What are the different shapes of medulla in human hair?
Absent, continuous, discontinuous, or fragmented
What is the medullary ratio? What are other names for this ratio? How does it differ between humans and animals?
- Ratio = Width(diameter) of medula / Width (diameter) of hair shaft
- Also called medullary estimate or index
- Medulla will make up more than 1/2 of diameter in animals when medulla is less than 1/3 for humans
What type of DNA is in the medulla? Where is it also found in the body? Which parent does it come from?
- Contains mDNA (Mitochondrial DNA)
- mDNA can also be found in your bones
- This type of DNA is passed down from your mom