DNA Report Glossary

Allele

An allele is one of several alternative forms of a DNA sequence occupying a given locus on a chromosome. Autosomal DNA has two alleles for each locus, one allele is inherited from the biological mother, and the other allele is inherited from the biological father. Y DNA has only one allele value for each locus because unlike the autosomal DNA, the Y-DNA is inherited only from the biological father and only one copy of the Y-DNA exists in each male individual (females do not have Y-DNA). STR testing of the Y-DNA involves the determination of the allele value at multiple loci to generate a haplotype. An individual’s haplotype can be used to trace ancestry along the male lineage. STR testing of autosomal DNA determines the allele values of DNA which is inherited from both the mother and the father and represents the unique mixture of STR markers inherited from many ancestors from both the mother and the father.

Autosome (Autosomal DNA, Autosomal Chromosome)

A chromosome that is not a sex chromosome, normally appearing in pairs in somatic cells. Humans have 23 pairs of chromosomes: 22 pairs of autosomal chromsomes and one pair of sex chromosomes (X and Y sex chromosomes). The X chrosomosome and Y chromosome are not autosomes.

Chromosome

A structure composed of a threadlike linear strand of DNA and associated proteins that carries part or all of the hereditary information of an organism. Humans have 23 pairs of chromosomes, 1 to 22 are autosomes and a pair of sex chromosomes (X and X for female, X and Y for male).

CODIS (COMBINED DNA INDEX SYSTEM)

CODIS is a distributed database system for documenting and comparing genetic profiles. CODIS specifies the following 13 autosomal DNA loci as a standard: (D3S1358, vWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317, D7S820, D16S539, THO1, TPOX, CSF1PO). Genetrack tests all CODIS loci and also 2 additional loci (D2S1338 and D19S433), resulting in a more informative result than using the CODIS loci alone.

Combined Paternity Index (CPI)

The CPI is calculated by multiplying the PI values for each independent locus and is the total paternity index for the loci examined. A CPI of 0 corresponds to a 0% probability of paternity (paternity exclusion) whereas a CPI of >1000 corresponds to a probability of paternity of >99.9% (paternity inclusion).

Deoxyribonucleic Acid (DNA)

The main component of chromosomes, the material that carries and transfers genetic information. The biological material that is transferred from parents to their children. The examination of DNA can provide information about relatedness and ancestry.

Genetic Profile (also, ‘DNA Profile’, or ‘DNA Fingerprint’)

The data obtained from a DNA test, represented by numbers. The genetic profile of an individual does not vary with the age or tissue type of that individual. The genetic profile can therefore be used in forensic investigations to determine if two samples are derived from the same person. Note that identical twins will share identical genetic profiles.

Grandparentage Index

A statistical likelihood ratio representing a comparison of the probability that the individuals are related versus the probability that the individuals are unrelated. A kinship index is calculated for each locus and is used to calculate the Combined Grandparentage Index.

Haplotype

A set of alleles on a single chromosome, such as the Y chromosome.

Hypervariable Region (HVR-1, HVR-2)

Specific regions of the mtDNA that do not code for protein. In humans, the HVR region typically contains a large number of mutations which can be used to derive ancestry. The entire mtDNA is 16,569 base pairs in length. The HVR1 region is found within base pairs 16001 to 16569, and the HVR2 region is found between base pairs 1 to 574. Testing the HVR1 and HVR2 regions of the mtDNA is usually the starting point for ancestral studies.

Kinship Index

A statistical likelihood ratio representing a comparison of the probability that individuals are related versus the probability that the individuals are unrelated. A kinship index is calculated for each locus and is used to calculate the Combined Kinship Index.

Locus (pl. loci)

Locus is a specific defined position on a chromosome. A locus may be characterized by any one of a different number of alleles.

Match Probability

The probability of a random match of a genetic profile within a population. For example, a match probability of 1:10 (i.e., 0.1) indicates that there is a 0.1 (i.e., 10%) chance of a random match in the population, whereas a match probability of 1:100 (i.e., 0.01) indicates that there is only a 0.01 (i.e., 1%) chance of a random match in the population. A 1:100 match probability is therefore a better indication that two samples are derived from the same individual than a match probability of 1:10.

Locus (pl. loci)

Circluar DNA present in the cytoplasm of a cell. In humans, mtDNA is present at 100 to 10,000 copies per cell and is inherited from the mother. mtDNA carries information about an individual’s maternal ancestry.

Mitochondrial DNA (mtDNA)

Locus is a specific defined position on a chromosome. A locus may be characterized by any one of a different number of alleles.

Paternity Index (PI)

A likelihood ratio representing a comparison of the probability that the alleged father is the biological father versus the probability that a random man in the population is the biological father. A PI is calculated for each locus and is used to calculate the combined paternity index and probability of paternity.

Polymerase Chain Reaction (PCR)

Technique for amplifying specific regions of DNA by multiple cycles of DNA polymerization. PCR is the method used by the DNA laboratory to amplify specific loci for analysis, and is capable of producing a genetic profile from very small amounts of sample.

Power of Exclusion (PE)

The ability of an assay to discriminate between a real match and a non-match.

Prior Probability

This is a value ranging from 0 (impossible) to 1 (absolute certainty). A prior probability value of 0.5 is commonly used.

Probability of Paternity

A statistical percentage based upon the combined paternity index and prior probability, describing the probability that the alleged father is the biological father of the child. A 0% probability of paternity indicates a paternity exclusion and a probability of paternity of 99.9% or greater is indicative of a paternity inclusion.

Relative Match Index (RMI)

The RMI is a measure of the likelihood that an individual belongs to a particular population as compared to all other populations.

Short Tandem Repeats (STR)

Identical repeated sequences of DNA. The variability in the numbers of repeats is often used as a method to distinguish between different individuals.

Sibling Index

A statistical likelihood ratio representing a comparison of the probability that the individuals are related as siblings (full or half) versus the probability that the individuals are unrelated. A sibling index is calculated for each locus and is used to calculate the Combined Sibling Index.

Somatic

The cells of the body with the exception of the reproductive cells (gametes). Examples of somatic cells are blood cells and buccal cells.

Y-DNA (Y chromosome)

One of the sex chromosomes. Males have one Y chromosome and one X chromosome. Females have two X chromosomes and do not have a Y chromosome. The Y chromosome is inherited from the father and carries ancestral information about an individual’s paternal line (e.g. father’s father’s father’s… line).