BI 140: Unit 1 Study Guide (Split Cards)

What are the scientific requirements for a forensic biology application to be accepted in the forensic field?

Validated by the 3 Rs, generally accepted in the field (published peer-reviewed papers), and uses standards/controls.

What are the legal requirements for a forensic biology application to be accepted in the forensic field?

Admissible in court under Frye or Daubert standards (Kansas adopted Daubert in 2014) and meets expert witness criteria (Kumho Tire).

What is a class characteristic?

Groups a sample with other similar samples (e.g., blood, saliva, fiber type).

What is an individual characteristic?

Unique to a single individual/source (e.g., nuclear STR DNA profile; identical twins are the only exception).

What is an unknown (U) or questioned (Q) sample?

Evidence collected from a crime scene whose source is unknown.

What is a known (K) reference sample?

Reference sample collected directly from a known individual (e.g., buccal swab, blood) for comparison.

What does robust mean in the three Rs of validation?

Works under a variety of conditions.

What does reliable mean in the three Rs of validation?

Consistently produces results.

What does repeatable mean in the three Rs of validation?

Produces the same results for the same sample.

What is the relationship between molecules, cells, tissues, and organisms?

Molecules form Organelles → form Cells → form Tissues → form Organs → form Organisms.

What is the role of enzymes?

Proteins that catalyze biochemical reactions by lowering activation energy. Examples: DNA polymerase (Taq) synthesizes DNA; nucleases break DNA bonds.

What are the 2 main reasons PPE should be worn at a crime scene or while handling potential evidence?

1. Protect investigators from exposure to bodily fluids/pathogens.
2. Prevent investigators from contaminating evidence with their own DNA.

When is a moistened swab (followed by a dry swab) used to collect a sample?

Dry stains on non-absorbent surfaces.

When is a dry swab used to collect a sample?

Wet stains (must air-dry before packaging).

When is cutting used to collect a sample?

Stains on absorbent substrates (fabrics, carpet).

When is scraping (druggist's fold) used to collect a sample?

Dried flakes; avoids substrate PCR inhibitors (e.g., indigo dye in jeans).

When is lifting tape used to collect a sample?

Lifts trace stains or hair from surfaces.

When is FTA paper used to collect a sample?

Liquid blood/saliva reference samples; lyses cells on contact.

What types of connections can evidence be used to make?

Victim-to-Perpetrator, Victim-to-Scene, Perpetrator-to-Scene.

What is the Locard exchange principle?

Cross-transfer of evidence occurs whenever a person contacts another person or object ("every contact leaves a trace").

How should dry evidence items be packaged to preserve them from contamination and degradation?

Package items separately in breathable paper bags.

How should wet items be stored to preserve them from contamination and degradation?

Air-dry wet items at room temperature without heat (heat/moisture cause mold and degrade DNA).

How should stained items be folded when storing evidence?

Do not fold directly over stains (put paper between folds).

How should liquid evidence be stored to preserve it from contamination and degradation?

Liquid evidence goes in sealed plastic containers and is refrigerated (not frozen).

What is the purpose of taking a control sample from a crime scene for comparison?

Taken from an unstained area adjacent to the stain to provide a baseline reference ensuring the substrate itself does not interfere with testing or cause false positives.

What is a chain of custody, and what can happen if it is broken?

A written record tracking who possessed, transferred, or analyzed evidence with dates and times. If broken or missing, the evidence can be thrown out of court.

What is the general structure of the DNA molecule?

Double-stranded, antiparallel (5' to 3' and 3' to 5') helix with a sugar-phosphate backbone and base pairs: A pairs with T, G pairs with C.

What type of DNA is found in the nucleus?

Nuclear DNA (nDNA; linear).

What type of DNA is found in the mitochondria?

Mitochondrial DNA (mtDNA; circular).

What is the size and chromosome number of the human genome?

~3.2 billion base pairs on 23 chromosome pairs (22 autosome pairs + 1 sex pair).

How is nuclear DNA (nDNA) inherited?

50% from mother (22 autosomes + X), 50% from father (22 autosomes + X/Y).

How is mitochondrial DNA (mtDNA) inherited?

100% maternally inherited from the mother.

What are gametes?

Sperm and egg; haploid (1n, 23 chromosomes).

What are somatic cells?

All other body cells; diploid (2n, 46 chromosomes).

What does diploid (2n) mean?

2 sets of chromosomes (46 total).

What does haploid (1n) mean?

1 set of chromosomes (23 total).

What does homozygous mean?

Two identical alleles at a locus (e.g., 12, 12).

What does heterozygous mean?

Two different alleles at a locus (e.g., 12, 14).

What are the characteristics of nuclear DNA (nDNA)?

Linear, 2 copies/cell, biparental inheritance.

How do the characteristics of nuclear DNA (nDNA) impact forensic analysis?

Unique to an individual (individualizing), degrades faster.

What are the characteristics of mitochondrial DNA (mtDNA)?

Circular, 100s–1000s copies/cell, maternal inheritance.

How do the characteristics of mitochondrial DNA (mtDNA) impact forensic analysis?

Shared by maternal relatives, highly resistant to degradation.

What percentage of blood is plasma, and what does it contain?

Plasma (55%): Fluid containing proteins, antibodies, cell-free nucleic acids.

What percentage of blood is the cellular fraction, and what does it contain?

Cellular fraction (45%): Red blood cells (erythrocytes), White blood cells (leukocytes), Platelets.

How are white blood cells (leukocytes) used in forensics, and what characteristic makes that possible?

Have nuclei; the only source of nuclear DNA in blood.

How are red blood cells (erythrocytes) used in forensics, and what characteristic makes that possible?

Nulliploid (no nucleus/DNA); contain hemoglobin (heme) targeted by serological presumptive/confirmatory tests.

What are transcellular fluids, and where does the target DNA in them come from?

Secretions in epithelial spaces (saliva, semen); target DNA comes from suspended cells (buccal cells, sperm).

What are extracellular nucleic acids, and where are they found?

Free-floating cell-free DNA/RNA found outside cells in plasma or sweat.

What are the layers of skin from outer to inner?

Epidermis → Dermis → Subcutaneous layer.

What are the sub-layers of the epidermis?

Cornified → Granular → Spinous → Basal.

Which skin layer is most likely to be left at a crime scene?

The cornified layer (dead, flattened, anucleate, keratinized cells).

What are the characteristics of the skin cells left at crime scenes in touch DNA samples, and how do they impact DNA analysis?

Shed cornified skin cells lack nuclei and organelles, resulting in very low DNA yields and a low profiling success rate (~12.4%).

What is the structure of a hair root?

Embedded in dermis; contains dividing nucleated cells.

What are the layers of a hair shaft from outside to inside?

Cuticle (outer scales) → Cortex (middle, contains pigment) → Medulla (central canal).

How does the structure of hair impact DNA analysis?

Hair keratinization causes nuclei to degrade. Hair shafts lack nuclear DNA but contain abundant mtDNA. The hair root is required for nuclear DNA analysis.

What is the anagen stage of the hair cycle?

Active growth (root has nDNA).

What is the catagen stage of the hair cycle?

Transitional phase (cell death begins).

What is the telogen stage of the hair cycle, and why does it matter forensically?

Resting phase; club hair sheds naturally. Most commonly left at crime scenes.

What is cortical (compact) bone?

Solid, dense outer layer.

What is the bone marrow cavity?

Inner hollow cavity filled with bone marrow.

What is the epiphysis?

Spongy (cancellous) bone at the ends of long bones.

Where in a bone is DNA located?

Inside osteocytes (bone cells) entrapped within the calcified matrix and within marrow cavity cells.

Why are bone and teeth more likely than softer tissues to be available in older or degraded samples?

They possess a hard inorganic matrix of hydroxyapatite crystals $[Ca_{10}(PO_4)_6(OH)_2]$ that protects organic collagens and cell DNA from decomposition, bacteria, and scavengers.

What type of DNA is found in the pulp cavity of a tooth?

Primary source of nuclear DNA (nDNA).

What type of DNA is found in dentin?

Contains mitochondrial DNA (mtDNA).

What type of DNA is found in cementum and cementoblasts?

Contains both nDNA and mtDNA.

Which part of a tooth is sampled for DNA, and why?

Root is sampled to preserve the crown for dental record comparisons.

Which sample types have high DNA profiling success rates (~86–92%), and why?

Semen & Blood (dense nucleated cells: sperm & WBCs).

Which sample types have moderate DNA profiling success rates (~37–73%), and why?

Cigarette butts, gum, saliva (shed nucleated buccal cells).

Which sample types have low DNA profiling success rates (~12–18%), and why?

Shed hair & Touch DNA (dead, anucleate, keratinized cells).

Why is it important to identify various sample types?

Associates evidence with specific crime types, establishes investigative linkages, proves intent, and screens evidence to locate stains for individualizing STR DNA testing.

What is a presumptive test?

Rapid, sensitive screening showing a sample could be a specific body fluid.

What is a confirmatory test?

Specific test proving conclusively what a sample is.

Why is each presumptive test presumptive and not confirmatory?

They lack absolute specificity and produce false positives (e.g., blood tests react with bleach, plant peroxidases, and metal salts; AP and amylase are present in other bodily fluids).

What do all of the presumptive blood tests detect, and how?

All detect the Heme moiety of Hemoglobin via catalytic oxidation.

How does the Kastle-Meyer presumptive blood test work?

Colormetric: Heme catalyzes phenolphthalin oxidation by hydrogen peroxide → Pink (alkaline).

How does the Leucomalachite Green (LMG) presumptive blood test work?

Colormetric: Heme catalyzes LMG oxidation by hydrogen peroxide → Blue-Green (acidic).

How does the Hemastix presumptive blood test work?

TMB strip + hydrogen peroxide + heme → Green.

How does the Luminol presumptive blood test work?

Heme catalyzes luminol oxidation → Blue chemiluminescence in dark.

How does the Bluestar presumptive blood test work?

Chemiluminescent spray visible in diffused light; DNA-safe.

How does the Fluorescein presumptive blood test work?

Reacts with heme; emits yellow-green fluorescence under ALS (425–485 nm).

What type of tests are the confirmatory blood tests, and what do they detect?

Microcrystal tests detecting Heme.

How does the Takayama (hemochromagen) confirmatory blood test work?

Pyridine + glucose + heme → Pink feathery crystals.

How does the Teichmann (hematin) confirmatory blood test work?

Glacial acetic acid + salts + heat → Brown rhombic crystals (best for aged stains).

How is ALS used as a presumptive test for semen, and what does it detect?

Detects flavin (seminal vesicles); fluoresces under 450–495 nm with orange goggles.

How does the Acid Phosphatase (AP) / Fast Blue B presumptive test for semen work?

AP cleaves phosphate, reacting with Fast Blue B → Purple in <1 min.

How does the Christmas Tree Stain confirm the presence of semen?

Stains spermatozoa; NFR stains heads red, PIC stains tails green.

How does the ABAcard PSA test confirm semen, and what does it detect?

Immunochromatographic strip detecting Prostate-Specific Antigen (PSA) (lines at T and C).

How is ALS used as a presumptive test for saliva, and what does it detect?

Detects amylase fluorescence at ~470 nm with orange goggles.

How is microscopy used as a presumptive test for saliva?

Visualizes shed buccal epithelial cells under magnification.

How does the Starch-Iodine presumptive test for saliva work?

Amylase digests starch; test is positive if iodine stays yellow (no blue-black).

How does the Phadebas presumptive test for saliva work?

Amylase digests starch-dye complex → releases blue color.

How does the RSID-Saliva test confirm saliva, and what does it detect?

Immunochromatographic strip detecting Human Salivary α-Amylase (HSA) (lines at T and

How do you know something is an enzyme?

ends in -ase