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Exam II. Chapters 16, 7, 13, 10 and 12, Labs 5, 6, 7/8 . Chapter 16 Fingerprints 1. What contributions did Henry Faulds , Francis Galton, Juan Vucetich and Edward Richard Henry each make to fingerprinting ?.

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Exam ii

Exam II

Chapters 16, 7, 13, 10 and 12,

Labs 5, 6, 7/8


Exam ii

Chapter 16 Fingerprints1. What contributions did Henry Faulds, Francis Galton, Juan Vucetich and Edward Richard Henry each make to fingerprinting?

  • Henry Faulds- claimed that fingerprints did not change over time and that they could be classified for identification

  • Francis Galton- developed a primary classification scheme based on loops, arches and whorls

  • Juan Vucetich- developed a fingerprint classification based on Galton’s that is used in Spanish-speaking countries

  • Edward Richard Henry- in collaboration with Galton instituted a numerical classification system


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2. Why are fingerprints considered individual evidence and what is the foundation for their acceptance in court?

  • A fingerprint is an individual characteristic because no two have yet been found to possess identical ridge characteristics.

  • The foundation for their acceptance in court:

    - The probability that two fingerprints could match is low.

    - There are an estimated 64 billion different individual prints.

    • This is supported by the millions of individuals who

      have had prints taken over the past 90 years in the FBI central system-- no two have ever been found to be identical!


3 what are fingerprints

3. What are fingerprints?

  • Fingerprints are a reproduction of friction skin ridges found on the palm of the fingers and thumbs.

  • Dermal papillae extend outward and determine the form and pattern of ridges on the surface.

  • Dermal papillae develop in the fetus and the ridge patterns remain unchanged throughout life except to enlarge during growth.

Figure 16-3 Cross section of human skin.


4 how does thin skin differ from thick or friction skin how does epidermis differ from dermis

4. How does thin skin differ from thick, or friction, skin? How does epidermis differ from dermis?

  • Skin is composed of layers of cells:

    - thin skin has 4 layers

    - thick/friction skin has 5 layers

  • Epidermis is superficial (outside) to the dermis, which is deep (inside).

Figure 16-3 Cross section of human skin.


5 be able to identify ridge characteristics or minutiae on a sample fingerprint

5. Be able to identify ridge characteristics, or minutiae, on a sample fingerprint.


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6. Be able to identify the general ridge patterns that allow fingerprints to be systematically classified:

  • A loop must have one or more ridges entering and exiting from the same side. Loops must have one delta.

  • Types

    • radial loop- opens toward the thumb

    • ulnar loop- opens toward the “pinky” (little finger)

Figure 16-5 Loop pattern.


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  • A plain whorl or central pocket whorl has at least one ridge that makes a complete circuit. A double loop is made of two loops. An accidental is a pattern not covered by other categories. Whorls have at least two deltas and a core.

    Figure 16-6 Whorl patterns.


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  • An arch has friction ridges that enter on one side of the finger and cross to the other side while rising upward in the middle. They do NOT have type lines, deltas, or cores.

    Figure 16-7 Arch patterns.


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7. Be able to calculate an individual’s primary classification numberwhen given the point values and equation.

Assign the number of points for each finger that has a whorl and substitute into the equation:

right

left

right right left left left

index ring thumb middle little + 1

=

right right right left left

thumb middle little index ring +1


8 what are latent prints

8. What are latent prints?

  • Latent fingerprints are those that are not visible to the naked eye. These prints consist of the natural secretions of human skin and require development for them to become visible.


9 what three glands provide the secretions for latent prints and how do they differ

9. What three glands provide the secretions for latent prints and how do they differ?

  • Eccrine- largely water with both inorganic (ammonia, chlorides, metal ions, phosphates) and organic compounds (amino acids, lactic acids, urea, sugars). Most important for fingerprints.

  • Apocrine- secrete pheromones and other organic materials.

  • Sebaceous- secrete fatty or greasy substances.


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10. Know some techniques for developing latent prints including powders, iodine, ninhydrin, silver nitrate, and cyanoacrylate.

  • Powders- adhere to both water and fatty deposits.

  • Iodine- fumes react with oils and fats to produce a temporary yellow brown reaction; can be fixed for at least several weeks with a 1% solution of starch in water

  • Ninhydrin- reacts with amino acids to produce a purple color.

  • Silver nitrate- reacts with chloride to form silver chloride, a material which turns gray when exposed to light

  • Cyanoacrylate- “super glue” fumes react with water and other fingerprint constituents to form a hard, whitish deposit.


11 what is sublimation

11. What is sublimation?

  • sublimation- solid that turns into a vapor without passing through a liquid phase

    e.g. iodine crystals


12 what other types of prints can be analyzed

12. What other types of prints can be analyzed?

  • Ears- shape, length and width

  • Voice- electronic pulses measured on a spectrograph

  • Foot- size of foot and toes; friction ridges on the foot

  • Shoes- can be compared and identified by type of shoe, brand, size, year of purchase, and wear pattern

  • Lips- display several common patterns like short vertical or horizontal lines, crosshatching and branching grooves

  • Teeth- bite marks are unique and can be used to identify suspects.

  • Eye- the blood vessel patterns in the eye may be unique to individuals


13 what is afis how was it improved by iafis

13. What is AFIS? How was it improved by IAFIS?

  • Automated Fingerprint Identification System (AFIS)- a computer system for storing and retrieving fingerprints that began in the 1970’s

  • By the 1990’s most large jurisdictions had their own systems in place. The problem: a person’s fingerprints may be in one AFIS but not in others.

  • IAFIS- the FBI’s Integrated Automated Fingerprint Identification system which is a national database of all 10-print cards from all over the country


14 what are biometrics and how can they be used

14. What are biometrics and how can they be used?

  • Use of some type of body metrics for the purpose of identification. (The Bertillon system may actually have been the first biometry system.)

  • Used today in conjunction with AFIS

  • Examples include retinal or iris patterns, voice recognition, hand geometry

  • Other functions for biometrics: can be used to control entry or access to computers or other structures, can identify a person for security purposes, can help prevent identity theft or control social services fraud.


Lab 5 fingerprinting 15 what are latent prints what are inked prints

Lab 5 Fingerprinting15. What are latent prints? What are inked prints?

  • Latent prints- not visible to the naked eye; must be developed to become visible

  • Inked prints- taken from an individual for identification purposes


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16. Why did running one of your thumbs or fingers down the side of your nose or through your hair help you make a latent print?

  • Pick up secretions from sebaceous glands as well as eccrine glands.


17 how were latent prints developed with powder and lifted

17. How were latent prints developed with powder and lifted?

  • Dip a soft fingerprint brush into the carbon black or aluminum fingerprint powder. Then tap it against the top of the powder jar to shake off the excess powder.

  • With a circular, sweeping motion that barely touches the slide, brush across the surface until you see the fingerprint begin to appear.

  • Once you see the fingerprint, apply powder in a direction that follows the ridge flow.

  • When the print is clearly developed, stop brushing (or you may destroy the fingerprint)!

  • If necessary, carefully shake off any excess powder from the slide over the powder jar or trash can.

  • Unwind a piece of clear tape about 10 cm in length and place the free end of the tape at a point about 7 cm from the top of the print on the slide. Smooth the piece of tape over the print with your finger, moving slowly from the free end of the tape to a point about 1 cm past the print.

  • When the print is entirely covered with tape, pull the whole piece of tape straight up at once, carefully removing the tape and print from the slide.

  • Transfer the print to a clean white index card.


18 what are the components of a fingerprint

18. What are the components of a fingerprint?


19 how are ninhydrin iodine and super glue used to detect latent fingerprints

19. How are ninhydrin, iodine, and super glue used to detect latent fingerprints?

  • ninhydrin- solution swabbed onto print; reacts with amino acids to produce a pink/purple color

  • iodine- print placed in fuming jar for 3-5 minutes; reacts with oils to produce yellow/brown color; then fixed in solution

  • super glue- print placed in fuming chamber for hours; polymerizes on secretions to produce white print


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Chapter 7 The Microscope20. What are the differences between a simple microscope, a compound microscope, and a stereoscope or dissecting microscope?

  • simple microscope- one lens

    e.g. magnifying lens

  • compound microscope- 2 lenses that “compound” or magnify each other

  • stereoscope or dissecting microscope- no special slide preparation necessary


21 know the functions and be able to label the following parts of a compound light microscope

21. Know the functions and be able to label the following parts of a compound light microscope:

  • eyepiece

    • the part of the microscope you look into

    • usually magnifies material being viewed by 10x

    • sometimes contains a pointer that can be seen as you look into the eyepiece

    • may also be called the ocular because it contains the ocular lens

    • may be monocular or binocular


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  • body tube

    - connects eyepiece to nosepiece

  • nosepiece

    • part of microscope to which the objectives are attached

    • rotates to allow for the changing of objectives to increase or decrease magnification


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  • objectives

    - scanning/low (4x)

    - medium (10x)

    - high (40x)

    - oil immersion (60x)


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  • arm

    • a secure part of the microscope to hold on to when the microscope is being carried


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  • stage

    - platform on which microscope slide rests

  • stage clip

  • mechanical stage/slide adjuster

    - used for adjusting the position of the slide for viewing


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  • coarse adjustment/focus knob

    - controls large movements of the stage or nosepiece

  • fine adjustment/focus knob

    - controls more precise focusing under higher powered objectives


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  • diaphragm

    - regulates the amount of light passing through the slide


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  • illuminator

    - light source

  • base

    - provides support for microscope


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22. Be able to calculate the total magnification when given the magnification of the ocular lens and an objective lens.

  • Total Magnification = Magnification of Ocular lens (10x) x Magnification of Objective Lens


23 what is the field of view and how does it change as magnification increases

23. What is the field of view and how does it change as magnification increases?

  • Field of View (FV) is the illuminated circle that you see when looking through the microscope.

  • As magnification increases, the size of the FV gets smaller.


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24. Be able to calculate the diameter of a field of view under a new objective when given the magnification and diameter of a field of view under another objective.

  • Step 1 Calculate the Increase in Magnification.

    New Objective

    Old Objective

  • Step 2 Divide the old FV by the increase in magnification calculated in Step 1.

    Old FV (microns)

    Increase in Mag


25 what is a comparison microscope

25. What is a comparison microscope?

  • comparison microscope- uses two stages and sets of objectives connected by one body tube to one eyepiece


26 what are electron microscopes

26. What are electron microscopes?

  • electron microscopes- use electrons to illuminate a specimen instead of light

    - Scanning Electron Microscope (SEM)

    - Transmission Electron Microscope (TEM)


Chapter 13 hairs fibers and paint 27 what is a hair follicle

Chapter 13 Hairs, Fibers and Paint27. What is a hair follicle?

  • Hair grows from a hair follicle, extending from its root or bulb, and continuing into the shaft before terminating at the tip.


28 what are the three layers of a hair and where are they located

28. What are the three layers of a hair and where are they located?

  • cuticle- outside covering formed by overlapping scales

  • cortex- thickest layer

  • medulla- inner row of cells


29 what scale patterns are found in the cuticles of humans and animals

imbricate

spinous

coronal

29. What scale patterns are found in the cuticles of humans and animals?

  • imbricate- human, dog

  • spinous- rabbit

  • coronal- cat

    Figure 13-2 Scale patterns of various types of hair.


30 in which part of the hair are pigment granules embedded

30. In which part of the hair are pigment granules embedded?

  • cortex-embedded with pigment granules whose color, shape and distribution provide important features for comparison


31 what patterns can be found in the medulla

31. What patterns can be found in the medulla?

  • medulla-humans may have a continuous, an interrupted, a fragmented, a solid, or no medulla

    Figure 13-4 Medulla patterns for various types of hair.


32 how do the medullary indexes differ between humans and animals

32. How do the medullary indexes differ between humans and animals?

  • The ratio of the diameter of the medulla relative to the diameter of the whole hair is called the medullary index (MI).

    - Human hair usually has an MI of 1/3 or less.

    - Animal hairs usually have an MI of ½ or more.


33 what are the three phases of hair growth and how do they differ

33. What are the three phases of hair growth and how do they differ?

  • anagen- growth phase that may last up to 6 years; root is attached to the follicle giving it a flame-shaped appearance

  • catagen- hair continues to grow, but at a decreasing rate for 2-3 weeks; root takes on an elongated appearance

  • telogen- hair growth ends and hair is pushed out of the follicle over a 2-6 month period; root has a club-shaped appearance

    Figure 13-6 Hair roots in the anagen phase, catagenphase, and telogen phase.


34 what part of the hair is best for dna analysis

34. What part of the hair is best for DNA analysis?

  • The follicular tag, when attached to the root,allows for the best DNA analysis.


35 how does nuclear dna differ from mitochondrial dna

35. How does nuclear DNA differ from mitochondrial DNA?

  • nuclear DNA- DNA present within the nucleus of a cell; inherited from both parents

    - obtained from follicular tags of hairs in the anagen or catagen phases

  • mitochondrial DNA- DNA present in organelles called mitochondria; only inherited from the mother

    - can be obtained from any hairs 1-2 cm in length


36 how many hairs are needed for a representative sample of head hair of pubic hair

36. How many hairs are needed for a representative sample of head hair? Of pubic hair?

  • The collection of 50 full-length hairs from all areas of the scalp will normally ensure a representative sampling of head hair.

  • A minimum collection of 24 full-length pubic hairs should cover the range of characteristics present in pubic hair.


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37. What is the difference between natural fibers and manufactured fibers? Be able to recognize examples of each.

  • Natural fibers- derived from animal or plant sources

    e.g. animal- wool, cashmere, fur

    plant- cotton

    Figure 13-8 Photomicrograph of cotton fiber.

  • Manufactured fibers- derived from either natural or synthetic polymers

    e.g. rayon (regenerated fiber), nylon (synthetic fibers)

    Table 13-1 Major Generic Fibers


38 what is a monomer what is a polymer

38. What is a monomer? What is a polymer?

  • monomer- subunit

  • polymer- chain of monomers

  • Figure 13-10 Starch and cellulose are natural carbohydrate polymers consisting of a large number of repeating units or monomers.


39 when can fiber evidence be individual evidence

39. When can fiber evidence be individual evidence?

  • If the analyst can fit pieces of fiber together at their torn edges, then the evidence becomes individual.


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40. How can class characteristics obtained from fibers aid in an investigation like the Wayne Williams’ case?

  • Fibers can be analyzed for characteristics such as color, cross- section, type and other features.

    Figure 13-13 A scanning electron photomicrograph of the cross section of a nylon fiber removed from a sheet used to transport the body of a murder victim. The fiber, associated with a carpet in Wayne Williams’s home, was manufactured in 1971 in relatively small quantities.


41 how should fiber evidence be collected and preserved

41. How should fiber evidence be collected and preserved?

  • The investigator’s task of looking for strands of fibers often becomes one of identifying and preserving potential “carriers” of fiber evidence.

  • Relevant articles of clothing should be packaged carefully in separate paper bags.

  • If it is necessary to remove a fiber from an object, the investigator must use clean forceps, place it in a small sheet of paper, fold and label the paper, and place the paper packet inside another container.


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Lab 6 Examination of Hair and Textile Fibers by Microscopy42. Be able to label the medulla, cortex and cuticle as in Figure 15-1.


43 be able to identify the scale patterns as in figure 15 2

43. Be able to identify the scale patterns as in Figure 15-2.


43 how do human hairs differ from animal hairs

43. How do human hairs differ from animal hairs?

  • Cuticle scale pattern

    - humans- imbricate; animals- imbricate,

    spinous or coronal

  • Medullary Index

    - humans 1/3 or less; animals ½ or more


45 what is the difference between a longitudinal section and a cross section

45. What is the difference between a longitudinal section and a cross section?

  • longitudinal section- view of long axis

  • cross-section- view of diameter


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Chapter 10 Forensic Serology46. How many different blood factors have been identified? Which are the most important?

  • There are more than 100 different surface blood factors.

  • The ABO factors are most important for matching a donor to a recipient.


47 why is blood important in forensic analysis

47. Why is blood important in forensic analysis?

  • No two individuals (except identical twins) can be expected to share all the 100+ blood factors.

  • There is a high frequency of occurrence of bloodstains at crime scenes, especially crimes of the most serious nature– that is, homicides, assaults, and rapes.


48 what are the components of blood

48. What are the components of blood?


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49. What are the different types of formed elements found in blood? How do white blood cells differ from red blood cells?

  • platelets- fragments of cells that help repair damaged blood vessels

  • leukocytes- WBCs; responsible for immunity

  • erythrocytes- RBCs; biconcave disks that contain oxygen-carrying hemoglobinprotein

    - discard their nuclei, mitochondria and most organelles during development.


50 what are antigens and antibodies

50. What are antigens and antibodies?

  • antigen- a substance, usually a protein, that stimulates the body to produce antibodies against it

  • antibody- a protein that binds to a specific antigen; produced by B lymphocytes


51 be able to determine the type of blood based on agglutination

51. Be able to determine the type of blood based on agglutination.

  • The interaction of antigens on red blood cells with specific antibodies carried in the plasma results in agglutination, the clumping together of red blood cells by the antibody.


52 what is the rh factor and how does it influence blood type

52. What is the Rh factor and how does it influence blood type?

  • The Rh factor was named after the Rhesus monkey.

  • If the Rh factor surface protein is present on red blood cells, the blood is Rh positive; otherwise it is Rh negative.


53 what is a gene what is a chromosome

53. What is a gene? What is a chromosome?

  • gene- a unit of inheritance consisting of a DNA segment located on a chromosome

  • chromosome- a piece of DNA wrapped around various proteins


54 know the terms karyotype autosome and sex chromosomes

54. Know the terms karyotype, autosome, and sex chromosomes.

  • karyotype- picture of a cell’s chromosomes

  • Human cells have 46 chromosomes divided into 23 pairs:

  • 22 pairs of autosomes

  • 1 pair of sex chromosomes


55 which sex chromosomes are found in normal females normal males

55. Which sex chromosomes are found in normal females? Normal males?

  • XX females

  • XY males


56 what are the female and male gametes what is a zygote

56. What are the female and male gametes? What is a zygote?

  • Female gametes, or sex cells, are called eggs.

  • Male gametes are called sperm.

  • At fertilization, the zygote is formed with 46 chromosomes.


57 what is a locus what is an allele

57. What is a locus? What is an allele?

  • locus- location of a gene on a chromosome

  • allele- alternative forms of genes


58 what do the terms homozygous and heterozygous mean

58. What do the terms homozygous and heterozygous mean?

  • homozygous- an individual has identical alleles for a gene

  • heterozygous- an individual has different alleles for a gene


59 what do the terms dominant and recessive mean

59. What do the terms dominant and recessive mean?

  • One allele may be dominant to the other that is recessive, or masked.

    e.g. Rh + allele is dominant to Rh - allele


60 what do the terms genotype and phenotype mean

60. What do the terms genotype and phenotype mean?

  • genotype- alleles present in an individual

  • phenotype- characteristic that results from genotype e.g. blood type


61 how does the kastle meyer color test indicate the presence of blood what are false positives

61. How does the Kastle-Meyer Color Test indicate the presence of blood? What are false positives?

  • When blood, phenolphthalein and hydrogen peroxide are mixed, the hemoglobin in the blood will turn the normally colorless phenolphthalein to a bright pink color.

  • false positives- materials other than blood (such as potatoes and horseradish) that also produce the bright pink positive result


62 what is luminol what are the advantages and disadvantages of using luminol

62. What is Luminol? What are the advantages and disadvantages of using Luminol?

  • Luminol is a chemical that, when mixed with hydrogen peroxide, exhibits chemiluminescencein the presence of a catalyst such as the iron in hemoglobin.


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Advantages

Disadvantages

Luminol glows even in the presence of certain other fluids-- semen, feces, bleach, tonic water, potatoes, etc.

  • Allows one to detect stains that would not ordinarily be visible.

  • Extremely sensitive-- can use it to detect very dilute concentrations.

  • CSIs can spray large areas with it.

  • It does not interfere with DNA, so a CSI can collect samples for DNA analysis even after they were sprayed with luminol.


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63. How do precipitin and gel diffusion tests indicate whether blood is from a human or a specific type of animal?

  • Antiserum against the specific type of blood (human, deer, dog, etc.) will react to specific antigens, forming a precipitate.

    Figure 10-8 Gel Diffusion Test


64 can the human immune system naturally detect the presence of drugs or other chemicals

64. Can the human immune system naturally detect the presence of drugs or other chemicals?

  • No.

  • The immune system only creates antibodies and launches attacks against foreign proteins (either free proteins or ones bound to cells) and not against other chemical compounds, like drugs.


65 what is the difference between polyclonal and monoclonal antibodies how are each produced

65. What is the difference between polyclonal and monoclonal antibodies? How are each produced?

  • Antigen is injected into an animal such as a rabbit.

  • The animal’s immune system will create antibodies that are specific to the shape of the antigen.

  • We can then isolate these antibodies from the animal’s blood serum.

  • polyclonal antibodies- antibodies that bind to a variety of sites on an antigen


Exam ii

  • monoclonal antibodies- antibodies that all recognize a single site on an antigen

  • A mouse is immunized against a specific antigen and then its spleen cells are fused with myeloma (cancer) cells.

  • Clones, groups of identical cells, are grown and each produces one type of monoclonal antibody.


66 what is emit and how is it used to detect marijuana metabolites in blood

66. What is EMIT and how is it used to detect marijuana metabolites in blood?

  • Enzyme-Multiplied Immunoassay Technique (EMIT)

  • Monoclonal antibodies for THC-9-carboxylic acid are added to the sample to be tested (blood, urine).

  • The antibodies will immediately bind to any THC-9-carboxylic acid molecules present in the sample.

  • Enzyme-labeled THC-9-carboxylic acid molecules are then added to the sample.

  • Any antibodies that did not bind to THC-9-carboxylic acid prior to this step (extra antibody molecules), will bind to the enzyme-labeled THC-9-carboxylic acid.

  • One can now measure the amount of unbound or unused enzyme-labeled THC-9-carboxylic acid to get a value of THC originally present in the sample.

  • more unbound enzyme-labeled THC-9-carboxylic acid = more THC-9-carboxylic acid originally present in sample


67 what is acid phosphatase and why is it used to detect semen

67. What is acid phosphatase and why is it used to detect semen?

  • Acid phosphatase is an enzyme secreted by the prostate gland into seminal fluid, where its concentration is 400x greater than those found in other body fluids.

  • When acid phosphatase comes in contact with a solution of sodium alpha napthylphosphateand Fast Blue B, a purple color appears.

  • However, some substances, including cauliflower, watermelon, fungi, contraceptive creams and vaginal secretions also give positive acid phosphatase results, though usually not as quickly or strongly.


68 what is oligospermia what is aspermia

68. What is oligospermia? What is aspermia?

  • oligospermia-males with abnormally low sperm counts

  • aspermia- males who do not produce sperm


69 what evidence is collected from a victim as part of a rape kit

69. What evidence is collected from a victim as part of a rape kit?

  • Appropriate items of physical evidence including clothing, hairs, and swabs can be collected for subsequent laboratory examination.

  • All outer and under garments should be carefully removed and packaged separately in paper (not plastic) bags.

  • Bedding, or the object upon which the assault took place, may also be carefully collected.


70 how does locard s exchange principle influence rape evidence

70. How does Locard’s exchange principle influence rape evidence?

  • The forceful physical contact between victim and assailant may result in a cross-transfer of such physical evidence as blood, semen, saliva, hairs, and fibers.

  • If a suspect is apprehended within 24 hours of the assault, it may be possible to detect the victim’s DNA on the male’s underwear or on a penile swab from the suspect.


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Chapter 12 Crime-Scene Reconstruction: Bloodstain Pattern Analysis71. How does surface texture influence bloodstains? What is satellite spatter?

  • The harder and less porous the surface, the less spatter that results.

  • satellite spatter- small droplets of blood that are distributed around the perimeter of a drop or drops of blood and were produced as a result of the blood impacting the target surface

    Figure 12-2 Bloodstain on glass surface versus cotton sheet.


72 how is the direction of travel determined from a bloodstain

72. How is the direction of travel determined from a bloodstain?

  • The pointed end of a bloodstain faces its direction of travel.

    Figure 12-3 Bloodstain pattern produced by drops of blood traveling from left to right.


73 how does the angle of impact influence bloodstains

73. How does the angle of impact influence bloodstains?

  • A drop deposited at an angle of 90°, directly vertical to the surface, will be approximately circular in shape.

  • As the angle of impact deviates from 90°, the stain becomes more elongated.

    Figure 12-4


74 how are the areas of convergence and origin determined from bloodstains

74. How are the areas of convergence and origin determined from bloodstains?

  • If you draw straight lines through the long axis of several blood stains, you can determine the area of convergence.

  • The area of origin may further be determined by considering the angle of impact.

    Figure 12-8


75 how do bloodstains resulting from arterial gush or spurt often appear

75. How do bloodstains resulting from arterial gush or spurt often appear?

  • Bloodstains resulting from blood exiting the body under pressure from a breached artery often show a pattern related to the heart beat.


76 how do cast off stains often appear and what can they reveal about a crime

76. How do cast-off stains often appear and what can they reveal about a crime?

  • Blood released or thrown from a blood-bearing object in motion (e.g. knives, bludgeons) often appears in an arc.

  • Can reveal whether assailant used left or right hand and how many times victim was struck.


77 what is impact spatter

77. What is impact spatter?

  • impact spatter- bloodstain patterns produced when an object makes forceful contact with a source of blood, projecting drops of blood outward from the source


78 what is the difference between forward and back spatter

78. What is the difference between forward and back spatter?

  • forward spatter- blood that travels away from the source in the same direction of the force that caused the spatter

  • back spatter- blood directed back toward the source of the force that caused the spatter


79 how do low velocity medium velocity and high velocity impact spatter differ

79. How do low-velocity, medium-velocity and high-velocity impact spatter differ?

  • low velocity- created by a force travelling at 5 feet/sec or less; produces relatively large stains greater than 4 mm in diameter

  • medium velocity- created by a force travelling at 5- 25 feet/sec; produces stains 1 – 4 mm in diameter; normally associated with blunt-force trauma

  • high velocity- created by a force travelling at 100 feet/sec or greater; produces stains with diameters less than 1 mm; normally associated with gunshot exit wounds or explosions


80 what is a transfer bloodstain and what can it reveal about a crime

80. What is a transfer bloodstain and what can it reveal about a crime?

  • A transfer bloodstain is created when a wet, bloody surface comes in contact with a secondary surface.

  • A recognizable image of all or a portion of the original surface may be observed in the pattern,as in the case of a bloody hand or footwear print.


Lab 7 8 blood 81 what is the difference between a presumptive test and a confirmatory test

Lab 7/8 Blood81. What is the difference between a presumptive test and a confirmatory test?

  • Initial tests are called presumptivetests because of their potential results. Presumptive tests can, at best, only strongly indicate that the tested substance is correctly assumed because other substances can also give a positive result.

  • Confirmatory tests do not usually give false positives. It is only after you have a positive result from a confirmatory test that you can make a positive identification of the substance.


82 be able to interpret the results of a kastle meyer test

82. Be able to interpret the results of a Kastle-Meyer Test.

  • clear- negative

  • pink, within 10 sec- positive for blood

  • color change earlier or later- false positive


83 be able to interpret the results of a blood typing test

83. Be able to interpret the results of a blood typing test.

  • When antibody binds antigen, agglutination (clumping) results.

  • No clumping indicates antibody does not bind to antigen.

    Type A blood clumps in anti-A serum

    Type B blood clumps in anti-B serum

    Type AB blood clumps in both anti-A and anti-B

    sera

    Type O blood does not clump in either anti-A or anti-B

    sera


84 how does luminol detect the presence of blood

84. How does Luminol detect the presence of blood?

  • Traces of blood can be detected when Luminol is prepared with hydrogen peroxide as a basic solution. When a catalytic amount of iron is provided from the hemoglobin in blood it will generate the blue chemical glow that is described as chemiluminescence.


85 how is the impact angle of blood calculated

85. How is the impact angle of blood calculated?

width of stain = sine of the impact angle

length of stain


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