Forensics Midterm Review Guide KEY

Unit 1: Introduction to Forensics

1. The Seven S’ in Order

  • Securing the Scene

    • Responsible: First responders, law enforcement

    • Action: Ensure the scene is safe and secure.

  • Separating the Witnesses

    • Responsible: Police officers

    • Action: Ensure witnesses do not communicate with one another to preserve their accounts.

  • Scanning the Scene

    • Responsible: Crime scene investigator

    • Action: Determine the primary and secondary scene locations for investigation.

  • Seeing the Scene

    • Responsible: Crime scene investigator

    • Action: Take overall photographs and consider evidence.

  • Sketching the Scene

    • Responsible: Crime scene investigator

    • Action: Create a rough sketch of the scene, marking important items.

  • Searching for Evidence

    • Responsible: Crime scene investigator

    • Action: Conduct a systematic search for physical evidence.

  • Securing and Collecting Evidence

    • Responsible: Crime scene investigator

    • Action: Properly collect and package evidence for analysis.

2. Primary vs. Secondary Scene

  • Primary Scene

    • Definition: The location where the crime actually occurred.

  • Secondary Scene

    • Definition: Locations related to the crime, where evidence may be found (e.g., a suspect's home).

3. Chain of Custody

  • Definition: The documented and unbroken transfer of evidence to ensure integrity and accountability.

4. Types of Evidence

  • Individual Evidence

    • Definition: Evidence that can be traced to a single source (e.g., DNA, fingerprints).

  • Class Evidence

    • Definition: Evidence that can be linked to a group of objects or persons (e.g., blood type).

  • Direct Evidence

    • Definition: Evidence that directly links an individual to the crime.

  • Circumstantial Evidence

    • Definition: Evidence that implies a fact or event without directly proving it.

  • Physical Evidence

    • Definition: Tangible objects collected from a crime scene.

  • Biological Evidence

    • Definition: Biological materials collected, such as blood, hair, or bodily fluids.

Unit 2: Fingerprints

5. Locard’s Principle of Exchange

  • Definition: The principle states that the perpetrator of a crime will bring something into the crime scene and leave with something from it, which can be used as forensic evidence.

6. Types of Fingerprints

  • Patent Fingerprints

    • Definition: Visible prints made by fingers coated in a substance (e.g., blood, ink).

  • Latent Fingerprints

    • Definition: Invisible prints left on surfaces, developed by dusting or chemical methods.

  • Plastic Fingerprints

    • Definition: Imprints left in soft substances (e.g., wax, dust).

7. Deltas in Fingerprint Patterns

  • Generally, loops have 1 delta, whorls have 2 deltas, and arches have 0 deltas.

8. Ridge Count and Database

  • Ridge Count: Method to determine the number of ridge lines between the core and a delta.

  • Fingerprint Database: Known as the Automated Fingerprint Identification System (AFIS).

Unit 3: DNA

9. Genes vs. Noncoding Areas of DNA

  • Genes: Segments of DNA that code for proteins.

  • Noncoding Areas: Segments that do not code for proteins but may have regulatory functions.

10. CODIS

  • Definition: Combined DNA Index System, used for matching DNA profiles.

11. Components of Nucleotide

  • Made up of:

    • A phosphate group,

    • A sugar (deoxyribose), and

    • A nitrogenous base (A, T, C, G).

12. Gel Electrophoresis

  • Purpose: To separate DNA fragments by size.

  • Process: DNA is loaded into a gel and an electric current runs through, causing smaller fragments to move faster than larger ones.

13. PCR (Polymerase Chain Reaction)

  • Purpose: To amplify DNA sequences.

  • Process: Involves repeated cycles of denaturation, annealing, and extension to create millions of copies of a specific DNA segment.

14. STR (Short Tandem Repeat)

  • Definition: A DNA sequence where patterns of two or more nucleotides are repeated.

  • Number of Markers: At least 13 markers must match to confirm a relationship.

15. Allele Frequency Calculation

  • Example: To calculate allele frequency for an allele number of 10, analyze the provided data from STR.

Unit 4: The Science of Blood

16. Blood Types

  • There are four main blood types: A, B, AB, and O.

  • Type of Evidence: Blood typing is considered class evidence.

17. Components of Blood

  • Mixture: Blood is composed of plasma, red blood cells, white blood cells, and platelets. The components combine to perform various functions in the body.

18. Antigens vs. Antibodies

  • Antigens: Substances that trigger an immune response, found on the surface of red blood cells.

  • Antibodies: Proteins produced by the immune system to identify and neutralize foreign objects.

19. Antigens for Each Blood Type

  • A+: Antigen A, Rh factor

  • B-: Antigen B

  • AB-: Antigens A and B

  • O+: Rh factor

  • O-: None (universal donor)

20. Blood Type Possibility for Mrs. Lane

  • If Mrs. Lane’s parents are A and B, she cannot be blood type O since she must inherit an A or B allele from one of her parents.

21. Probability of Offspring Blood Types

  • If one parent is AB and the other is O, the possible blood types for their offspring are A (50% probability) and B (50% probability).

22. Impact of Height on Blood Shape

  • When blood is dropped from different heights, the shape becomes more circular, and the number of spines increases with height. Increased spines and satellites indicate higher impacts.

23. Angle of Impact Analysis

  • When blood is dropped at different angles, the shape elongates; a larger angle results in a wider blood smear while smaller angles produce more acute shapes. Calculate the angle of impact using trigonometric formulas based on the shape observed.