Chapter 18 Hair PDF

Preview

Summary

Chapter 18 Notes from Crime and Forensics taught by Professor Forsthoff. ...

Description

●

●

What is Hair? ○ Hair is an outgrowth of the epidermis,  or  outer layer of the skin. ○ It is found only in mammals. ○ Follicles are the structures from which hairs originate and grow. ○ When hair begins to grow, its outer covering is soft. ○ When it reaches the top of the skin, the outer layer begins to harden into k eratin. ○ Keratin is made of proteins; it is the same material that makes up fingernails and toenails in humans and horns in other animals. ○ Inside the follicle, where the hair is growing, it is enervated by blood vessels that provide nourishment and which exchange materials between blood and the inside of the hair. ○ Anything that is ingested by the person, such as food, drugs, or poisons, will eventually be incorporated into the growing region of the hair. ○ When the hair reaches the surface of the skin and keratinizes, it is essentially dead. ○ When hair grows, it is really being “pushed up” by the growing part of the hair in the follicle. ○ It is analogous to the size of a stack of dinner plates growing taller by continuously adding more plates to the bottom of the stack. Hair Growth ○ Most tissues grow in a smooth, regular fashion. ○ Anyone who observes his or her hair growing out after cutting would assume that hair also grows like this, but such is not the case. ○ The active growing period of hair is called the a  nagen p  hase. ○ The follicle produces new hair cells that are added to the shaft of the hair, thus pushing the hair up the follicle toward the surface of the skin. ○ After the anagen phase is complete, the next phase begins. ○ This is the c  atagen p  hase. ■ It is a transition between growth and rest. ○ Cell production in the follicle declines and the root of the hair shrinks into a bulb-like shape. ○ In the telogen  phase, the hair has stopped growing completely. ○ It will stay this way until the hair is lost by pulling (combing or brushing) or shedding. ○ Hairs lost in one of these ways will contain the root. ○ Forcible Removal of Hair ■ Sometimes hairs are forcibly removed by yanking or tearing or by violent contact and are also left at scenes. ■ It is often important to know whether a hair was shed or removed. ■ The amount of cellular material on the root depends on how fast the hair was pulled. ■ If the hair is pulled quickly, the chances of finding cells from the follicle are increased.

●

●

Hair Color ○ As hair grows, special cells called melanocytes  produces granules of melanin. ○ Melanin is the pigments that gives hair its color. ○ There are two types of melanin, one is dark brown and the other is lighter, almost blond. ○ These granules are dispersed throughout the middle layer of the hair (the cortex). ○ When hair is dyed, the melanin does not take up the dye, instead, the dye coats the surface of the hair. Structure of Human Hair ○ Scalp hairs are more often found at crime scenes than any other type so they will be used to illustrate the structure of human hairs. ○ Hairs from other parts of the body differ in systematic ways from head hair, and a competent hair examiner can distinguish among hairs from various parts of the body. ○ The root  is at the widest end of the hair and is the part that is attached to the follicle and is the growing area of the hair. ○ The second region is the s  haft. ○ From the root to the tip, the shaft tapers. ○ The tip is  the end of the hair away from the root; the hair is the narrowest at the tip. ○ This means that one must be careful in describing the diameter of a hair; it depends upon where it is measured. ○ The outermost layer of the hair is the c  uticle. ○ Is it made of keratin, the same material that makes up finger and toenails and is responsible for the stability and inertness of hair. ○ The cuticle is not a smooth layer like the painter outer surface of a pencil. ○ Instead, it consists of a series of overlapping scales arranged much like the shingles on a roof. ○ The middle layer of the hair is the c  ortex. ○ In humans, this is the most prominent and thickest layer. ○ The cortex is made up of spindle-shaped cells and is also transparent. ○ Pigment granules are dispersed throughout the cortex; these granules are generally not spaces in an even pattern but instead are often found in clumps. ○ They vary from person to person in size and shape as well as distribution. ○ The cortex also contains c  ortical fusi. ○ These are small bubble-like structures; their appearance may be related to the transition from anagen to catagen growth phase of hair. ○ Ovoid bodies, w  hich look like large pigment granules may also be present in the cortex. ○ The innermost layer of the hair is the m  edulla. ○ It is made up of cells that form a shaft through the middle of the hair. ○ In human head hair, the medulla may be totally absent, or it may be present in a few areas of the hair, or it may be mostly present, except for a few gaps.

●

●

●

Human versus Nonhuman Hairs ○ Many animals possess three different types of hair. ○ The first are called g  uard hairs. ○ These are firm hairs with a protective function; they have distinct features that make them useful for forensic purposes. ○ They are most often used for microscopic comparison. ○ The rest of the animal’s coat is filled in with with fur hairs. ○ These are relatively featureless and do not provide much information about the type of animal. ○ Finally, there are whiskers; whiskers are sensitive to touch and are used by the animal for sensory purposes. ○ Even though animal hairs differ from human, they still mostly contain the same three layers, cuticle, cortect, and medulla. Hair Treatment and Damage ○ When hair is dyed, it has a painted appearance, and there is an abrupt color change between the natural color and the dyed color. Comparison of Human Hairs ○ Hair evidence is found in a great variety of crimes. ○ Most commonly, it is evidence at scenes of crimes of violence such as criminal sexual assault. ○ In these types of crimes, pubic hairs from the victim and from the perpetrator will often be found on each other and the surface where the attack took place as well as surrounding areas. ○ This is especially powerful evidence since it demonstrates the transfer of two types of evidence between perpetrator and victim. ○ Hair is easily transferred from one surface to another and may undergo several transfers after being shed. ○ In the majority of cases, either head or pubic (or both) hairs are left as evidence at crime scenes. ○ It is important to get a sufficient number of known hairs and they must represent the head or pubic area as a whole. ○ There are natural variations of morphological characteristics of hairs within the same head or other area of the body. ○ If there are sufficient common characteristics between the knowns and unknowns and there are no unexplainable significant differences, than the hair examiner can conclude that the unknown hairs could have originated from the person who provided the known samples. ○ It merely states that the known could be the source of the unknown hairs. ○ Lacking a proper database of how common different types of hair are, the analyst cannot ascribe a probability to the association of the known and unknown hairs. ○ If the known and unknown samples exhibit significant differences that exceed the range of variation within a set of hairs, then the conclusion would be that the known donor could not have been the source of the unknown hairs.

●

●

What Can be Determined from the Structure of Hair? ○ As we have seen, a great deal can be determined from the structural analysis of hair. These include the following: ■ Human or Animal ● It is easy to determine if a hair is human or animal especially head hair. ■ Part of the body ● For human hair, it is usually not difficult to determine what part of the body hairs came from. ● Most crime scene hairs are either from the head or the pubis. ■ Color ● Hair that has been colored has more of a painted look than hair with a natural color. ● The natural color is due to clusters of melanin whereas dyed hair has a coating to the surface. ■ Disease ● Diseased or teased or artificially straightened or curled hair can usually be detected under a microscope. ○ There are also a number of characteristics that some people believe that hair can reveal. This, however, is generally not true. Some of these are listed as follows: ■ Age ● Age cannot be determined from the examination of hair. ● The fact that hair is gray does not mean that the person is old. ■ Gender ● At one time, perhaps 50 years ago, people may have concluded that long hair was female. ■ Race ● There are some racial characteristics of hair that show up if the person has fairly pure racial ancestry. DNA Analysis of Hair ○ Except for the root, hair does not contain sufficient nucleated cells to perform genomic DNA analysis, but hair cells do contain mitochondria and mitochondrial DNA typing is now routinely done on hair samples. ○ Mitochondrial DNA is inherited only through the maternal line. ○ It is becoming clear that microscope analysis and mitochondrial DNA analysis are complementary techniques that can both be valuable in the analysis of hair. ○ Since the maturation of mitochondrial DNA analysis, many hair examiners including those of the FBI have developed a protocol for the analysis of hair that employs both structural analysis and mitochondrial DNA analysis....