Ch.15 Forensic Serology

What is the A-B-O system and why is it no longer used by forensic scientists

A system for classifying blood types; no longer used because DNA provides far more accurate individual identification.

What is an antigen and how is it useful in individualizing blood

A protein that stimulates antibody production; the pattern of antigens on blood cells allows comparison and differentiation of blood samples.

What is an antibody and what happens when it reacts with its specific antigen

A protein that inactivates a specific antigen; reaction forms cross-linked cells causing visible clumping (agglutination).

What factor is most whole blood typed for and which blood types are most and least common in the U.S.

Most blood is typed for A-B-O; type O is most common and type AB is least common.

For what other application are antigen-antibody reactions used, and what is EMIT's main use and limitation

Used to detect drugs in blood and urine; EMIT is used to screen for marijuana but cannot determine when the drug was taken because positive results may appear up to ten days later.

Difference between monoclonal and polyclonal antibodies and which are more useful

Monoclonal bind to one antigen site; polyclonal bind to many. Monoclonal are more useful because they can target specific substances like drugs.

What three questions must be answered when examining dried blood

Is it blood? From what species? If human, how closely can it be associated with a particular individual?

List two commonly used color tests for blood and how luminol differs

Kastle-Meyer and Hemastix are color tests; luminol produces light, not color.

Purpose of a precipitin test and three strengths

Determines whether blood is human or animal; very sensitive, requires little blood, and works on dried stains years old.

What is a genotype and how do parents' genotypes affect offspring blood type and in what legal area this matters

Genotype is an individual's gene combination; children cannot inherit a blood type gene not present in either parent; important in paternity cases.

What is acid phosphatase and how is it used

An enzyme from the prostate found in semen; used to detect seminal fluid.

List three reasons spermatozoa may not be found in semen at a crime scene

They bind tightly to fabric, are brittle and disintegrate when dry or washed, and some males have low or zero sperm count.

Why investigators must ask about recent consensual sexual activity in sexual assault cases

Semen or acid phosphatase from consensual activity may still be present, affecting interpretation of evidence.

Forensic Serology

The examination of blood, semen, and saliva for forensic purposes.

ABO Blood Typing System

Blood classification based on A and/or B antigens on red blood cells.

Rh Factor

A blood antigen determining whether a person is Rh positive or negative.

Blood Antigen Systems

Multiple human blood antigen systems; ABO and Rh are the most important.

Type A Blood

Has A antigens and anti-B antibodies.

Type B Blood

Has B antigens and anti-A antibodies.

Type AB Blood

Has A and B antigens and no anti-A or anti-B antibodies; universal recipient.

Type O Blood

Has no A/B antigens and both anti-A and anti-B antibodies; universal donor (O−).

Antigen

A substance that triggers formation of antibodies.

Antibody

A protein that reacts specifically with a corresponding antigen.

Antigen-Antibody Reaction

Highly specific binding used in blood and drug testing.

Immunoassay

A test using antibodies to detect the presence of drugs or biological markers.

EMIT (Enzyme-Multiplied Immunoassay Technique)

A fast and sensitive immunoassay for detecting drugs in urine.

Kastle-Meyer Test

A presumptive test for blood that turns pink in the presence of hemoglobin.

Luminol Test

A chemiluminescent test used to visualize trace blood.

Precipitin Test

Determines whether blood is human or animal.

Individualizing Bloodstains

Using DNA analysis to link blood to a single individual.

Acid Phosphatase Test

A color test for seminal fluid; turns purple in the presence of the enzyme.

Spermatozoa

Sperm cells that conclusively identify semen.

p30 / PSA (Prostate-Specific Antigen)

Protein marker used to identify semen.

Motile Sperm (Persistence)

Present for 4-6 hours after intercourse.

Non-Motile Sperm (Persistence)

May persist for 3-6 days.

Seminal Acid Phosphatase (Persistence)

Detectable for under 48 hours.

Prostate Specific Antigen (Persistence)

Detectable for under 72 hours.

Pubic Combings

Hair combed from the victim to collect foreign hairs.

Pubic Hair Controls

~25 reference pubic hairs collected from the victim.

External Genital Swab

Swab collected from the outer genital area for biological evidence.

Vaginal Swab

Swab collected from inside the vagina for semen or DNA evidence.

Cervix Swab

Swab taken from the cervix to collect deeper biological material.

Rectal Swab

Swab used in cases involving possible anal penetration.

Oral Swab

Swab used to collect saliva or semen from the mouth.

Head Hair Controls

~25 reference head hairs taken from the victim.

Buccal Swab

Cheek swab used to obtain a DNA reference sample.

Fingernail Scrapings

Material collected from beneath the nails for possible assailant DNA.

Urine Specimen

Sample taken for drug-facilitated assault testing.

Clothing Evidence

All garments collected and packaged separately in paper bags.

Bedding Evidence

Sheets or materials from the assault site collected for testing.

Biological Evidence Photography

Requirement to photograph evidence before collecting it.

Latex Gloves

Must be worn to prevent contamination when handling biological material.

No Plastic Packaging

Biological evidence must not be stored in plastic due to moisture and bacterial growth.

Paper Packaging

Stained items must be packaged individually in paper bags or ventilated boxes.

Refrigerated Storage

Biological samples must be kept cool until sent to the lab.