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DNA & Fingerprints
EXAM 2 ADV FORENSICS
| Question | Answer |
|---|---|
| Why is DNA such a useful forensic tool? | DNA is stable, identical in almost all cells, persists in degraded samples, and varies by ~0.1% between individuals |
| What is a locus? | A specific position on a chromosome |
| What is an allele? | a variant form of a gene at a given locus |
| Homozygous vs Heterozygous | Homozygous = same alleles; Heterozygous = different alleles |
| How many chromosome pairs do humans have? | 23 pairs (22 autosomes + 1 sex chromosomes) |
| What does allelic frequency represent? | The proportion of a specific allele in a population |
| Why is allelic variation important? | It maintains species diversity and enables adaptation |
| Formula for possible genotypes? | k(k+1)/2 |
| Which bases pair together? | A-T and C-G |
| What charge does DNA carry? | Negative because of the phosphate groups |
| What is semi-conservative replication? | New DNA keeps one original strand |
| What determines DNA movement in gel? | Size (smaller fragments move faster) |
| How are DNA bands visualized? | Ethidium bromide with UV light |
| What does RFLP stand for? | Restriction Fragment Length Polymorphism |
| What caused RFLP variations? | Changes in restriction sites or VNTR differences |
| Disadvantages of RFLP? | Slow, requires large sample, not good with degraded DNA |
| Three major steps in DNA profiling? | Sampling, Analysis, Interpretation |
| What enzyme digests proteins in extraction? | Proteinase K |
| What is DTT used for? | Breaking disulfide bonds (sperm extraction) |
| What is the purpose of differential extraction? | To separate epithelial cells from sperm cells |
| Which cells lyse first? | Epithelial cells |
| What is an STR? | Short Tandem Repeat (short repeated DNA sequence) |
| How is an STR genotype shown? | Two numbers showing repeat count (8,8 = homozygous; 4,10 = heterozygous) |
| How many STR loci in modern CODIS? | 20 |
| Who invented PCR? | Kary Mullis in 1983 |
| PCR requirements? | Primers, DNA, dNTPs, polymerase, Mg++, buffer |
| Why is PCR useful? | Amplifies tiny amounts of DNA or degraded DNA |
| Name PCR inhibitors | Blood (heme), Hair (melanin), Bone (calcium), Saliva (polyamines), Urine (Urea), Feces (Bacteria) |
| What is mtDNA used for? | Degraded samples, bones/teeth, hair |
| What is Y-STR profiling? | Male-lineage STR analysis |
| What tech differentiates identical twins? | Rare SNP sequencing |
| What is familial DNA searching? | Finding relatives of a suspect through partial matches |
| What databases are used? | 23&Me, Ancestry.com, etc. |
| What is random match probability? | The likelihood that two unrelated people share a DNA profile |
| What model calculates genotype frequency? | Hardy-Weinburg |
| Multiplication rule? | Multiply genotype probabilities across loci |
| What does Daubert evaluate? | Reliability & admissibility of evidence in court |
| Name two Daubert criteria | Peer review, testing, error rates, acceptance |
| What creates fingerprints? | Friction ridges |
| When do fingerprints form? | Weeks 13-17 of fetal development |
| Do identical twins share fingerprints? | NO |
| Level 1 of fingerprint detail? | Ridge flow (arch/loop/whorl) |
| Level 2? | Minutiae: endings, bifurcations, islands |
| Level 3? | Sweat pores and ridge edges |
| Three pattern types? | Arches, loops, whorls |
| Most common pattern type? | Loops (~60-65%) |
| What determines fingerprint individuality? | Number, type, and arrangement of minutiae |
| What does ACE-V stand for? | Analysis, Comparison, Evaluation, Verification (from an expert) |
| What is a latent print? | Invisible print from sweat/oils |
| What does ninhydrin detect? | Amino acids (paper) |
| Purpose of superglue fuming? | Develop prints on nonporous surfaces |
| What is AFIS? | American Fingerprint Identification System |
| What is NGI? | Next-Generation Identification (prints, palms, facial ID, iris) |
| What can MALDI-MSI detect? | Drugs, metabolites, deposition timeline in prints |
| What is the name for a visible print? | Patent |
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