Forensic DNA & RNA Exam Mastery Vocabulary Flashcards

A complete set of vocabulary flashcards covering DNA/RNA biology, enzymes, contamination factors, lab extraction methods, and forensic result interpretation based on the lecture objectives.

DNA (Deoxyribonucleic acid)

Known as the 'blueprint of life,' it is the genetic material in the nucleus, inherited from parents, that determines individual characteristics.

Two Primary Functions of DNA

1. Information storage and inheritance (stable archive). 2. Directing protein synthesis (master code).

RNA (Ribonucleic acid)

The nucleic acid that serves as a mobile transcript, carrying DNA's instructions from the nucleus to the cytoplasm for protein production.

Chromosome

A tightly coiled thread of DNA, proteins, and RNA; humans typically have $46$ chromosomes ($23$ pairs).

Gene

A distinct sequence of nucleotides forming part of a chromosome that encodes for a single protein or RNA molecule.

Central Dogma

The three-step pipeline of genetic information flow: DNA $\rightarrow$ RNA $\rightarrow$ protein.

Transcription

The process where the DNA master code is copied into messenger RNA (mRNA).

Translation

The process where a ribosome reads mRNA to build a protein from $20$ amino acids.

Mitochondrial DNA (mtDNA)

DNA located in the mitochondria that is present in high copy numbers, resists degradation, and links individuals to a common maternal ancestor.

Deoxyribose

The five-carbon sugar found in DNA that is lacking one oxygen atom compared to ribose.

Ribose

The five-carbon sugar found in RNA that contains an extra oxygen ($OH$ group).

Purines

The larger, double-ring nitrogenous bases, which include Adenine ($A$) and Guanine ($G$).

Pyrimidines

The smaller, single-ring nitrogenous bases, which include Cytosine ($C$), Thymine ($T$), and Uracil ($U$).

A-T Hydrogen Bonding

A pairing held together by $2$ hydrogen bonds, making it weaker and easier to separate with heat than C-G pairs.

C-G Hydrogen Bonding

A pairing held together by $3$ hydrogen bonds, providing greater thermal stability and requiring higher heat to denature.

mRNA (messenger RNA)

The 'blueprint' RNA that carries the genetic code from the nucleus to the ribosome.

tRNA (transfer RNA)

The 'delivery truck' RNA that fetches specific amino acids and delivers them to the ribosome in the order specified by mRNA.

rRNA (ribosomal RNA)

The 'construction equipment' RNA that forms the structural and catalytic core of the ribosome.

Autosomal DNA

DNA found on the $22$ pairs of non-sex chromosomes; used in forensics because it is unique to every individual except identical twins.

Allele

The characteristic or value of a single copy of a specific location on a chromosome (e.g., the number of repeats at an STR locus).

Locus

The specific physical physical location of a gene or DNA marker on a chromosome.

Genotype

The designation of the two alleles present at a particular locus (e.g., $13, 16$).

DNA Polymerase (Taq)

A heat-stable enzyme from heat-tolerant bacteria used in PCR to build complementary DNA strands by reading a template.

RNA Polymerase II

The major enzyme responsible for transcription; it unzips DNA and incorporates RNA building blocks to create an mRNA transcript.

Restriction Enzymes

Known as 'molecular scissors,' these enzymes cut DNA at specific recognition sequences; used in older RFLP methods.

Proteinase K

An enzyme used during organic extraction to digest proteins and histones, thereby freeing the DNA from the cell structure.

PCR Primers

Short DNA sequences that act as 'address labels,' telling the DNA polymerase exactly where to start copying target regions.

Improper PPE

A contamination factor where failure to wear gloves or lab coats allows the investigator's own DNA to reach the evidence.

Cross-contamination

The transfer of DNA between two different evidence sources or via an uncleaned tool (e.g., an investigator's pen).

Chain-of-Custody

The unbroken, documented trail of evidence transfer; gaps like missing signatures can make evidence inadmissible in court.

Time Sensitivity

The only contamination factor not fully within human control; it refers to the inherent degradation clock and lab backlogs.

Organic Extraction

A versatile, gentle extraction method using SDS and phenol/chloroform; DNA is recovered from the aqueous (top) layer.

Chelex Extraction

A fast, Bio-Rad patented method that produces PCR-ready DNA but is too harsh for old, degraded, or fragile samples.

Differential Extraction

An extraction method for sexual-assault mixtures that uses a two-step wash to separate epithelial DNA from sperm DNA.

DTT (Dithiothreitol)

A reducing agent used in differential extraction to break disulfide bonds and lyse the tough outer membrane of sperm cells.

Inclusion (Match)

A result where a suspect's profile matches evidence at every locus; reported as 'cannot be excluded' using population statistics.

Exclusion

An absolute result where any single mismatch at a locus conclusively rules out a suspect as the source of the DNA.

Inconclusive

A result where bands are too faint, partial, or contaminated to make a call; requires repeating or retesting the sample.

Amelogenin (AMEL)

A sex-determination marker where $X, X$ indicates a female contributor and $X, Y$ indicates a male contributor.

Short Tandem Repeat (STR)

Multiple copies of a short DNA sequence arranged in succession; these are the markers used for forensic profiling.

CODIS

The FBI's database software that evaluates $13$ core STR loci to identify or link criminal suspects.

Homozygous

A genotype where both alleles at a locus are the same value, appearing as a single peak on an electropherogram (e.g., $16, 16$).

Heterozygous

A genotype where the two alleles at a locus are different, appearing as two distinct peaks (e.g., $13, 15$).

Decimal Allele (e.g., 9.3)

A notation indicating a micro-variant or slight mutation caused by a partial repeat sequence at a locus.