DNA Dictionary
There are lots of words used in DNA testing that you might not have heard before, so we’ve put together a DNA dictionary to help!
Accreditation: the process of officially recognising that an organisation is competent to perform specific activities in a reliable and accurate manner.
Affidavit: a written statement confirmed by oath or affirmation, for use as evidence in court.
Allele: one of several different forms of a DNA marker (see also locus). Humans have two alleles at each genetic marker, with one allele inherited from each parent.
Allele frequency: the incidence of an allele at a particular locus in a population. The allele frequency is calculated by dividing the number of times the allele is seen in a population by the total number of all alleles at that locus.
Autopsy sample: a sample that has been collected during the post-mortem examination of a deceased person.
Autosomal DNA: DNA carried on the autosomal chromosomes. Humans have 22 pairs of autosomal chromosomes and one pair of sex chromosomes. Autosomal DNA is inherited from both parents.
Buccal Sample: a gentle, non-invasive sample collected from the inside surface of the cheek.
Chromosome: the structure by which information is transmitted from one generation to the next. There are two types of chromosomes: autosomes and sex chromosomes. Humans have 23 pairs of chromosomes: 22 pairs of autosomes (numbered 1-22) and one pair of sex chromosomes (X and Y). Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father.
Deoxyribonucleic acid (DNA): a recipe that provides the instructions for telling our bodies how to develop and function. DNA consists of two strands that wind around each other to form a double helix, which is somewhat like a ladder. The information in DNA is stored as a code in four smaller molecules called bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order of these bases determines how the organism grows, like the way letters appear in certain order to form words and sentences.
Dizygotic twins: also known as fraternal twins, result from the fertilisation of two separate eggs during the same pregnancy. They share half of their DNA, just like any other siblings.
Exclusion: the alleged parent is not the biological parent. Exclusions are based on contradictions of the laws of genetic inheritance across multiple genetic markers, that is, the parent and child do not share DNA information at all locations tested.
Full siblings: individuals with both biological parents in common. Full siblings share an average of 50% of their DNA.
Genetic Marker (locus): a specific physical location on a chromosome, like a genetic street address. The plural of locus is loci.
Genotype/DNA profile: the genetic makeup of an organism; the alleles that are carried by an organism. The DNA profile for an individual consists of the genotypes for a set of genetic markers.
Half siblings: individuals with one biological parent in common, but not both. Half siblings share an average of 25% of their DNA.
ISO 17025: the international standard that describes the requirements a laboratory must meet in order to generate valid results.
Kinship analysis: examination of the relatedness between people using DNA markers. Depending on the circumstances of the case, autosomal DNA markers and/or Y-STR markers might be used. As the genetic distance between individuals increases, the evidential strength of the analysis decreases.
Legal DNA test: testing where samples have been collected by an appropriate medical professional and the identities of the people involved in testing have been confirmed. When samples have been collected in this way they meet the requirements of the Family Law Regulations and the results can be used for legal purposes, such as in Family Law disputes, and for changing birth certificates.
Likelihood Ratio: compares two probabilities to find out which probability is more likely, for example, are two people full siblings vs unrelated.
Maternal: something that originates from the mother of an individual, e.g. the maternal allele is inherited from the mother.
Maternity test: examination of whether a woman is the true biological mother of a child using DNA markers.
Monozygotic twins: identical twins resulting from the fertilisation of a single egg that splits in two. Identical twins share all their DNA, and are always the same sex.
Mutation: a genetic event where an allele changes from parent to child resulting in an apparent inconsistency in an alleged biological relationship.
National Association of Testing Authorities (NATA): the authority that provides independent assurance of a laboratory’s ability to produce reliable technical results.
Paternal: something that originates from the father of an individual, e.g. the paternal allele is inherited from the father.
Paternity test: examination of whether a man is the true biological father of a child using DNA markers.
Paternity Index (PI): the ratio of the chance that the tested man, given the DNA evidence, is the biological father compared to the chance that a random man is the biological father. The minimum PI to establish paternity is 1,000. A PI of 1,000 means that the tested man is 1,000 times more likely to be the biological father than a random, unrelated man in the population.
Patrilineal: relating to or based on relationship to the father or descent through the male line.
Peace of mind or at home test: testing where samples have been collected by you in your own home. As the identities of the people involved in testing have not been confirmed by an independent person, the results cannot be used for legal purposes. They are simply for your own information. These tests are not endorsed by NATA.
Probability of Paternity: the probability that the alleged father is the biological father of the child, expressed as a percentage. Takes into account both genetic and non-genetic information. The minimum probability of paternity to establish paternity is 99.9%.
Putative father: a man who is alleged to be or claims to be the biological father of a child.
Short tandem repeat (STR): short sequences of DNA that are repeated numerous times. Defined as a number indicating the number of repeats in the allele, e.g. the sequence ATCG repeated twelve times would give an allele of 12. STRs are highly variable between people, which is why they are so useful in human identification.
X chromosome: one of the two sex chromosomes in humans. Females have two X chromosomes, and males have one.
Y chromosome: one of the two sex chromosomes in humans. Females do not possess a Y chromosome, and males have one. The Y chromosome passes down from father to son.