Forensic DNA Exam – STR Markers, Isoalleles & Commercial STR Typing Kits |Verified Questions Provided with A+ Graded Rationales Latest Updated 2026

Forensic DNA Exam – STR Markers, Isoalleles & Commercial STR Typing Kits |Verified Questions Provided with A+ Graded Rationales Latest Updated 2026 STR sequences account for ____ % of the human genome 3 Preferential amplification During PCR, when alleles are very different in size, the shorter allele is amplified more resulting in an imbalance of peak heights or allele dropout Which size of STR repeats (# of nucleotides) are most preferable? Tetranucleotides What are 2 reasons why STRs are read by tetranucleotide repeat units? 1. reduced stutter 2. reduces preferential amplification during PCR Dinucleotide repeats produce ____ (low/high) stutter products. high Hexanucleotide repeats produce ____ (low/high) stutter products. low Isoalleles alleles with the same number of repeats (same length) but different sequences and are indistinguishable with STR typing Simple repeats contain units of identical length and sequence Simple repeats with non-consensus alleles most units contain identical length and sequence, but at least one allele will have missing BP(s) i.e. (GATA)(GAT-)(GATA) Compound repeats comprise two or more adjacent simple repeats (GATA)(GATA)(GACA) Complex repeats contain several repeat blocks of variable unit length (GATA)(GACA)(CA)(CATA) Microvariants alleles that contain incomplete repeat units (Allele 9.3 in TH01) What are 2 advantages for using STR markers in forensics? 1. small product sizes are generally compatible with degraded DNA 2. multiplex amplification enables high power of discrimination National DNA Index System (NDIS) FBI-operated database system that contains DNA profiles of convicted criminals and profiles of DNA collected from crime scenes Combined DNA Index System (CODIS) the FBI's computerized criminal DNA databases as well as the software used to run these databases; includes the National DNA Index System (NDIS) What are 3 reasons CODIS expanded the core loci from 13 to 20? 1. Reduce likelihood of adventitious matches 2. Increase discriminatory power 3. Increase international compatability Adventitious match a match between two DNA profiles by chance Amelogenin locus for sex identification, with the Y chromosome being 6 bp longer What are the components of the Pre-PCR mix in a STR typing kit? 1. primer mix (fluorescently labeled) 2. PCR reaction buffer 3. dNTPs 4. DNA polymerase 5. control DNA What are the components of the Post-PCR mix in a STR typing kit? allelic ladder Wh