Chapter 15
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What types of evidence would help an investigator substantiate that a sexual assault occurred?
Evidence includes: Seminal stains (acid phosphatase test, spermatozoa, or p30 protein) Pubic hair, head hair Swabs (vaginal, rectal, oral) Clothing (outer/undergarments) Bedding, DNA from the suspect
What are possible sources of DNA?
Blood, semen, saliva Skin cells, hair, bone Sweat, urine, touch DNA
What items might contain DNA?
Clothing, bottles/cans, weapons Cigarettes, envelopes, mattresses Door handles, steering wheels
How many bases are associated with DNA? What is the correct base-pairing sequence?
Four bases: Adenine (A) pairs with Thymine (T). Cytosine (C) pairs with Guanine (G).
What is luminol, and what is characteristic of its properties?
Luminol is a chemical test for blood detection. It produces luminescence in a dark area and can detect blood diluted up to 100,000 times.
What are buccal cells, and where are they obtained from?
Buccal cells are epithelial cells obtained from the inside of the cheek.
What does a precipitin test help determine about a bloodstain?
Whether the blood is of human origin.
Why is STR analysis the most significant DNA profiling procedure?
Requires only 125 picograms of DNA Works with degraded samples Provides a high degree of discrimination
How many cells are needed to obtain an STR profile?
Approximately 18 cells.
What is the most significant advantage of PCR testing?
PCR amplifies small DNA quantities, making it possible to analyze degraded or minute samples.
What is CODIS, and what does it enable forensic scientists to do?
CODIS (Combined DNA Index System): Compares DNA from crime scenes with profiles of known offenders or other unsolved crimes.
What are the Forensic Index and Offender Index in CODIS?
Forensic Index: Profiles from crime scenes Offender Index: Profiles of convicted individuals
What tests can tentatively identify blood?
Kastle-Meyer test (pink color) Benzidine derivative test (blue color) Luminol
What are best practices for avoiding contamination of DNA evidence?
Use PPE, change gloves frequently Use disposable instruments Air dry evidence Avoid plastic packaging; use paper bags
What is a “pseudo known”?
An item reasonably expected to contain DNA from a suspect (e.g., cigarette, straw), used when no reference sample is available..
What is mitochondrial DNA, and what are its characteristics?
Inherited maternally Useful for hair and degraded samples Shared by all maternal relatives
How should blood-containing clothes be packaged?
Air dry Package in paper bags Store in a cool location
What are moral and ethical concerns around DNA collection?
Privacy rights of individuals Misuse or false accusations based on partial DNA matches Use of kinship profiles
How can seminal stains be identified?
Acid phosphatase (purple color) Presence of p30 protein or spermatozoa
What does forensic genetic genealogy involve?
Uses public genealogy databases and consumer DNA profiles to identify suspects in cold cases.