The Study of Hair

The Study of Hair CSI at MDI Mr. Lurvey Hair as Evidence  Hair is one of the most common forms of trace evidence! Often sticks to clothes and is transferred to other locations (secondary transfer) Do you remember Locard’s Principle? (He liked hair a lot)   Most people lose between 40 and 125 hairs/day. Evidence Type?   Hair is Class Evidence (material that connects an individual or thing to a certain group) Hair could be Individual Evidence (ID a particular person) only if the follicle is present to allow DNA analysis Ouch! Dyed Hair, What’s it good for?   Only mammals have hair! For – Temperature regulation – Reducing friction – Protection from light – Sensing organ A Hair Follicle  A human body has about 5 million hair follicles when born As you age they decrease:( Only 100,000 are on the scalp (at 1000 strands/square inch)   Structure of A Hair  Hair shaft made of the protein keratin (a protein is a chain of amino acids with strong peptide C-N bonds)  Keratin is the same ingredient in your fingernails and toenails  Color is pigment called melanin The Structure of a Hair Hair is made of 3 layers: Cuticle, Cortex, Medulla Cuticle – outer coating composed of overlapping scales Cortex – protein-rich structure around the medulla that contains pigment Medulla – central core (may be absent) EVERY other slide in this PowerPoint has what for a Background Design?       This PPT Slide Design Template is called Writing Table Note the pencil to the left! The 3 layers of a hair are comparable to the layers in a pencil: Cuticle? Cortex? Medulla? Cuticle • Made of overlapping scales that point down hair •Human texture is imbricate (flattened) pattern •In humans this layer does not contain pigments (unless dyed) •Useful to tell different species - but not tell individuals apart Animal cuticles are different exterior and may have pigments Cortex • The cortex varies in: • Thickness • Texture • Color • Distribution of pigments • The cortex is used in determining from which individual a human hair may have come. Medulla • The medulla may vary in: • Thickness - Humans = less than one-third of total hair diameter (animals are more) • Continuity (4 types) •Absent •Fragmented •Intermittent •Continuous Can use Hair to tell Different Races (In General)  European  Asian  African What do you see here? razor cut abraded broken scissor cut Treated Hair    Dying Hair colors the cuticle and cortex Hair grows 1.3 cm/month (.44mm/day) New growth is not dyed If person had hair natural from root to dyed area was 2.6 cm They had their hair dyed ~ when? Roots hairs fall out naturally or can be forcibly removed What do we have here? double medulla post-mortem root band burned pubic hair Animal hairs? bat cat dog deer