Glossary of Terms

Alleles – In terms of Short Tandem Repeats or STRs, they are short sequences of DNA that are located on a chromosome. Each sequence is repeated a certain number of times. The number of times that the sequence repeats is an allele. For example if the sequence AATG repeats 7 times then the allele would be 7.
Chromosomes – Segmented packages of DNA found in the nucleus of the cell. Each person has 23 pairs of chromosomes in his or her cells. One set comes from the mother, one comes from the father.
CODIS 13 Loci – This is referring to the FBI’s Combined DNA Index System and the 13 core STR markers.
Differential Extraction – An extraction method for separating the sperm cells from the epithelial cells (skin cells) in an evidence sample.
Evidence – An item or sample submitted for testing that may contain biological material from an unknown source.
Exclusion – The individual associated with the DNA profile obtained from a reference sample is not a possible contributor to the DNA profile obtained from the evidentiary sample.
Identical Twins – One fertilized egg splits into two embryos that have the same genetic material, therefore a set of identical twins will have the same STR DNA profile.
Inclusion – The DNA profile obtained from an individual’s reference sample statistically matches the DNA profile obtained from an unknown evidentially sample.
Locus – This term is refers to the location on a chromosome. There are 2 alleles for each locus (one from mother, one from father). The plural form is loci.
Major Component – In a mixed profile the individual that contributes the most DNA to the mixture.
Minor Component – In a mixed sample the individual(s) that contribute less DNA to the mixture.
Quality Assurance Standards for Forensic DNA and Convicted Offender DNA Databasing Laboratories – The quality assurance standards serve as a benchmark for the assessment of the quality practices and performances of DNA laboratories across the country. Compliance with the standards are monitored by audits, which are performed internally by each laboratory as well as externally by multiple organizations including ASCLD/LAB, FQS-I, NYS-DOH and NFSTC.
Reference Sample – A known biological sample, usually in the form of a blood or buccal (cheek cell) sample, collected from an individual.
Trace Evidence – This refers to very small amounts of DNA that can be collected at the crime scene.