Collecting Blood Stains at the Crime Scene

Collecting blood stains at the crime scene

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Biological materials such as blood, body fluids and hair are identified and compared using forensic DNA analysis, microscopic analysis and biochemical methods.

Services provided by the Biological Section of a forensic science laboratory include :

identification of biological materials; forensic DNA analysis; macroscopic and microscopic hair comparisons.
Biological materials such as blood, body fluids and hair are identified and compared using forensic DNA analysis, microscopic analysis and biochemical methods.

Services provided by the Biological Section of a forensic science laboratory include :

  • identification of biological materials;
  • forensic DNA analysis;
  • macroscopic and microscopic hair comparisons.

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The most prominent application of DNA typing has been in identifying perpetrators of violent crime by comparison of biological samples of suspects against biological specimens that perpetrators have directly left at or taken from crime scenes (e.g. semen, saliva, skin, or blood).

DNA typing, however, is useful not only in cases where the victim cannot identify the perpetrator. Since most violent crime occurs between people who are acquainted or related, it can corroborate claims of, for example, sexual abuse where there is immediate disclosure (e.g. semen in victim’s vagina). In cases where the victim is pregnant or has given birth, the foetal or child’s DNA profile can be compared to the mother’s and the suspect’s to determine paternity. Interpretations of this sort are possible because DNA is inherited both maternally and paternally. In this way victims may be identified from the analysis of DNA in partially recovered remains or information provided on missing persons from the analysis of trace smears and "reverse paternity" interpretation.
The most prominent application of DNA typing has been in identifying perpetrators of violent crime by comparison of biological samples of suspects against biological specimens that perpetrators have directly left at or taken from crime scenes (e.g. semen, saliva, skin, or blood).

DNA typing, however, is useful not only in cases where the victim cannot identify the perpetrator. Since most violent crime occurs between people who are acquainted or related, it can corroborate claims of, for example, sexual abuse where there is immediate disclosure (e.g. semen in victim’s vagina). In cases where the victim is pregnant or has given birth, the foetal or child’s DNA profile can be compared to the mother’s and the suspect’s to determine paternity. Interpretations of this sort are possible because DNA is inherited both maternally and paternally. In this way victims may be identified from the analysis of DNA in partially recovered remains or information provided on missing persons from the analysis of trace smears and "reverse paternity" interpretation.

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DNA in the Human Body

DNA in the human body

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PCR Analysis

PCR analysis

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Forensic entomologists study insect life on or near bodies to determine the time and/or date of death. Only a few hours after death, flies and other insects are attracted to bodies and begin to lay eggs in the ears, eyes, nose, mouth or open wounds. Within days or hours, these eggs quickly grow into different stages of their life cycle (called instars). Different species of flies grow at different rates. The entomologist will take samples of the insect larvae and cultivate them to verify what species they are. Before the entomologist takes them he/she will determine the stage in their life cycle of the maggots or flies. Once he/she knows the species, and given the stage of their life at which they were found, the entomologist can determine how many hours/days the body has been exposed. The insect life that will appear on the body varies with the season, surroundings (i.e. geographical location) and other factors.
Forensic entomologists study insect life on or near bodies to determine the time and/or date of death. Only a few hours after death, flies and other insects are attracted to bodies and begin to lay eggs in the ears, eyes, nose, mouth or open wounds. Within days or hours, these eggs quickly grow into different stages of their life cycle (called instars). Different species of flies grow at different rates. The entomologist will take samples of the insect larvae and cultivate them to verify what species they are. Before the entomologist takes them he/she will determine the stage in their life cycle of the maggots or flies. Once he/she knows the species, and given the stage of their life at which they were found, the entomologist can determine how many hours/days the body has been exposed. The insect life that will appear on the body varies with the season, surroundings (i.e. geographical location) and other factors.

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Larva, Pupa, and Adult (L.-R.)

Larva, pupa, and adult (L.-R.)

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Physical evidence routinely examined includes: paint, fire debris, clothing and footwear, glass, fibres and textiles, safe insulation, soil, explosive debris and a wide range of commercial products. The examination of exhibits may be classified into two categories: (1) the identification of an unknown substance, and (2) the comparison of "known" and "questioned" exhibits.

Services provided by the Chemistry Section of a forensic science laboratory include :
recovering, comparing and identifying non-biological trace evidence (paint, fire debris, glass, clothing and footwear, plastics, building products, safe insulation, soil, explosives and post-blast debris and commercial products; physical matching of any of the seized materials; provision of scientific and user support of shared instrumentation (FTIR.SEM/EDX).
Physical evidence routinely examined includes: paint, fire debris, clothing and footwear, glass, fibres and textiles, safe insulation, soil, explosive debris and a wide range of commercial products. The examination of exhibits may be classified into two categories: (1) the identification of an unknown substance, and (2) the comparison of "known" and "questioned" exhibits.

Services provided by the Chemistry Section of a forensic science laboratory include :
  • recovering, comparing and identifying non-biological trace evidence (paint, fire debris, glass, clothing and footwear, plastics, building products, safe insulation, soil, explosives and post-blast debris and commercial products;
  • physical matching of any of the seized materials;
  • provision of scientific and user support of shared instrumentation (FTIR.SEM/EDX).

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Trace Evidence on a Jacket

Trace evidence on a jacket

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Learning Objectives

The learner will:
  • Develop enthusiasm and continuing interest in the study of science
  • Describe how the field of genetics relates to forensic science
  • Describe how biology and chemistry are used to solve crimes
  • Describe examples of the application of technology in society

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