Glossary of Terms
Accrediting organization for paternity testing. (Formerly known as the American Association of Blood Banks)
Certification by an official body ensuring a laboratory meets specific quality and accuracy standards.
Adenine (A) is one of the four nucleotide bases in DNA, with the other three being cytosine (C), guanine (G) and thymine (T). Within a double-stranded DNA molecule, adenine bases on one strand pair with thymine bases on the opposite strand. The sequence of the four nucleotide bases encodes DNA’s information.
The man who is claimed to be the biological father but whose paternity has not yet been confirmed.
A variant form of a gene; inherited from both biological parents.
Alternative splicing is a cellular process in which exons from the same gene are joined in different combinations, leading to different, but related, mRNA transcripts. These mRNAs can be translated to produce different proteins with distinct structures and functions — all from a single gene.
An amino acid is the fundamental molecule that serves as the building block for proteins. There are 20 different amino acids. A protein consists of one or more chains of amino acids (called polypeptides) whose sequence is encoded in a gene. Some amino acids can be synthesized in the body, but others (essential amino acids) cannot and must be obtained from a person’s diet.
Aneuploidy is an abnormality in the number of chromosomes in a cell due to loss or duplication. In humans, aneuploidy would be any number of chromosomes other than the usual 46.
A codon is a DNA or RNA sequence of three nucleotides (a trinucleotide) that forms a unit of genetic information encoding a particular amino acid. An anticodon is a trinucleotide sequence located at one end of a transfer RNA (tRNA) molecule, which is complementary to a corresponding codon in a messenger RNA (mRNA) sequence. Each time an amino acid is added to a growing polypeptide during protein synthesis, a tRNA anticodon pairs with its complementary codon on the mRNA molecule, ensuring that the appropriate amino acid is inserted into the polypeptide.
Antisense is the non-coding DNA strand of a gene. In a cell, antisense DNA serves as the template for producing messenger RNA (mRNA), which directs the synthesis of a protein.
A test where the biological specimens are collected in a non-clinical setting without the usual Chain of Custody procedures. Results from an at-home collection are not intended for use in legal matters. These tests are not governed by accrediting organizations.
An autopsy sample is one which is collected by a coroner or medical examiner during the examination of a body after death. Such samples usually consist of a blood sample.
Autosomal DNA is the DNA derived from all of the chromosomes (22 pairs in total) except the sex chromosomes (X & Y). A routine STR test involves the examination of a small percentage of the total autosomal DNA. The autosomal DNA examined in a DNA paternity test is non-coding, meaning that the DNA tested is not responsible for the generation of any physical characteristics of the person.
Autosomal dominant is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the mutated gene (from one parent) is enough to cause the disorder. A child of a person affected by an autosomal dominant condition has a 50% chance of being affected by that condition via inheritance of a dominant allele. By contrast, an autosomal recessive disorder requires two copies of the mutated gene (one from each parent) to cause the disorder. Huntington’s disease is an example of an autosomal dominant genetic disorder.
Autosomal recessive is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Recessive” means that two copies of the mutated gene (one from each parent) are required to cause the disorder. In a family where both parents are carriers and do not have the disease, roughly a quarter of their children will inherit two disease-causing alleles and have the disease. By contrast, an autosomal dominant disorder requires only a single copy of the mutated gene from one parent to cause the disorder. Sickle cell anemia is an example of an autosomal recessive genetic disorder.
An autosome is one of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (XX or XY). Autosomes are numbered roughly in relation to their sizes. The largest autosome — chromosome 1 — has approximately 2,800 genes; the smallest autosome — chromosome 22 — has approximately 750 genes.
A base pair consists of two complementary DNA nucleotide bases that pair together to form a “rung of the DNA ladder.” DNA is made of two linked strands that wind around each other to resemble a twisted ladder — a shape known as a double helix. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) [GWA-NeeN] or thymine (T). The two strands are held together by hydrogen bonds between pairs of bases: adenine pairs with thymine, and cytosine pairs with guanine.
Sometimes called Birth Father or the Natural Father. The Biological Father normally contributes 50% of his DNA to the child.
BRCA1 and BRCA2 are the first two genes found to be associated with inherited forms of breast cancer and ovarian cancer. People with mutations in either BRCA1 or BRCA2 have a much higher risk for developing breast, ovarian or other types of cancer than those without mutations in the genes. Both BRCA1 and BRCA2 normally act as tumor suppressors, meaning they help to regulate cell division. Most people have two active copies of these genes. When one of the two copies becomes inactive due to an inherited mutation, a person’s cells are left with only one copy. If this remaining copy also becomes inactivated, then uncontrolled cell growth results, which leads to breast, ovarian or other types of cancer.
This type of sample is collected using cotton-tipped applicators that are rubbed inside a person’s mouth on the inner lining of the cheek. The samples which are collected are cheek cell samples, not saliva samples. Also known as a cheek swab.
Cancer is a disease in which some of the body’s cells grow uncontrollably. There are many different types of cancer, and each begins when a single cell acquires a genomic change (or mutation) that allows the cell to divide and multiply unchecked. Additional mutations can cause the cancer to spread to other sites. Such mutations can be caused by errors during DNA replication or result from DNA damage due to environmental exposures (such as tobacco smoke or the sun’s ultraviolet rays). In certain cases, mutations in cancer genes are inherited, which increases a person’s risk of developing cancer.
A cancer-susceptibility gene is a gene that, when changed (or mutated), gives an individual an increased risk for developing cancer. Individuals who have inherited mutations in certain cancer-susceptibility genes have a lifetime risk of cancer that is significantly higher than the general population (e.g., BRCA1/BRCA2 ). Individuals in the high-risk category may benefit from more frequent cancer screens. There are also many gene variants associated with a small increase in risk. In some cases, environmental factors may also play a role.
The term candidate gene refers to a gene that is believed to be related to a particular trait, such as a disease or a physical attribute. Because of its genomic location or its known function, the gene is suspected to play a role in that trait, thus making it a candidate for additional study.
A carcinogen is a substance, organism or agent capable of causing cancer. Carcinogens may occur naturally in the environment (such as ultraviolet rays in sunlight and certain viruses) or may be generated by humans (such as automobile exhaust fumes and cigarette smoke). Most carcinogens work by interacting with a cell’s DNA to produce mutations.
A carrier, as related to genetics, is an individual who “carries” and can pass on to its offspring a genomic variant (allele) associated with a disease (or trait) that is inherited in an autosomal recessive or sex-linked manner, and who does not show symptoms of that disease (or features of that trait). The carrier has inherited the variant allele from one parent and a normal allele from the other parent. Any offspring of carriers is at risk of inheriting a variant allele from their parents, which would result in that child having the disease (or trait).
A legal process ensuring DNA samples are collected, handled, and tested securely for court-admissible results.
A structure containing DNA that carries genetic information from parents to children.
Cloning, as it relates to genetics and genomics, involves using scientific methods to make identical, or virtually identical, copies of an organism, cell or DNA sequence. The phrase “molecular cloning” typically refers to isolating and copying a particular DNA segment of interest for further study.
A DNA database used by law enforcement, though not typically relevant to private paternity tests.
Codominance, as it relates to genetics, refers to a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual. That is, instead of one trait being dominant over the other, both traits appear, such as in a plant or animal that has more than one pigment color.
A contig (as related to genomic studies; derived from the word “contiguous”) is a set of DNA segments or sequences that overlap in a way that provides a contiguous representation of a genomic region. For example, a clone contig provides a physical map of a set of cloned segments of DNA across a genomic region, while a sequence contig provides the actual DNA sequence of a genomic region.
Copy number variation (abbreviated CNV) refers to a circumstance in which the number of copies of a specific segment of DNA varies among different individuals’ genomes. The individual variants may be short or include thousands of bases. These structural differences may have come about through duplications, deletions or other changes and can affect long stretches of DNA. Such regions may or may not contain a gene(s).
CRISPR (short for “clustered regularly interspaced short palindromic repeats”) is a technology that research scientists use to selectively modify the DNA of living organisms. CRISPR was adapted for use in the laboratory from naturally occurring genome editing systems found in bacteria.
Crossing over, as related to genetics and genomics, refers to the exchange of DNA between paired homologous chromosomes (one from each parent) that occurs during the development of egg and sperm cells (meiosis). This process results in new combinations of alleles in the gametes (egg or sperm) formed, which ensures genomic variation in any offspring produced.
Cytosine (C) is one of the four nucleotide bases in DNA, with the other three being adenine (A), guanine (G) and thymine (T). Within a double-stranded DNA molecule, cytosine bases on one strand pair with guanine bases on the opposite strand. The sequence of the four nucleotide bases encodes DNA’s information.
Custody is a legal term used, most often in a divorce or separation, to describe who will have legal control and responsibility for a minor child. Legal custody may be granted to a single individual or to both parents (called joint or shared custody).
The Combined Paternity Index is the product of individual paternity indices at each genetic locus tested in a paternity test. The Combined Paternity Index compares the likelihood that the tested, mother and alleged father produced the child versus the likelihood that the mother and a man selected at random from the population produced the child. It is a measure of the weight of the scientific evidence obtained from the test.
Congenital refers to a condition or trait that exists at birth. Congenital conditions or traits may be hereditary or result from an action or exposure occurring during pregnancy or at birth, or they may be due to a combination of these factors.
A deletion, as related to genomics, is a type of mutation that involves the loss of one or more nucleotides from a segment of DNA. A deletion can involve the loss of any number of nucleotides, from a single nucleotide to an entire piece of a chromosome.
Diploid is a term that refers to the presence of two complete sets of chromosomes in an organism’s cells, with each parent contributing a chromosome to each pair. Humans are diploid, and most of the body’s cells contain 23 chromosomes pairs. Human gametes (egg and sperm cells), however, contain a single set of chromosomes and are said to be haploid.
Twins that are from two separately fertilized eggs. Also called Fraternal twins
The molecule that carries genetic instructions and determines biological relationships.
DNA fingerprinting is a laboratory technique used to determine the probable identity of a person based on the nucleotide sequences of certain regions of human DNA that are unique to individuals. DNA fingerprinting is used in a variety of situations, such as criminal investigations, other forensic purposes and paternity testing. In these situations, one aims to “match” two DNA fingerprints with one another, such as a DNA sample from a known person and one from an unknown person.
Specific regions of DNA used in genetic testing to establish relationships.
DNA replication is the process by which the genome’s DNA is copied in cells. Before a cell divides, it must first copy (or replicate) its entire genome so that each resulting daughter cell ends up with its own complete genome.
DNA sequencing refers to the general laboratory technique for determining the exact sequence of nucleotides, or bases, in a DNA molecule. The sequence of the bases (often referred to by the first letters of their chemical names: A, T, C, and G) encodes the biological information that cells use to develop and operate. Establishing the sequence of DNA is key to understanding the function of genes and other parts of the genome. There are now several different methods available for DNA sequencing, each with its own characteristics, and the development of additional methods represents an active area of genomics research.
A test that compares DNA samples directly between two individuals (e.g., father and child).
Double helix, as related to genomics, is a term used to describe the physical structure of DNA. A DNA molecule is made up of two linked strands that wind around each other to resemble a twisted ladder in a helix-like shape. Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T). The two strands are connected by chemical bonds between the bases: adenine bonds with thymine, and cytosine bonds with guanine.
Down syndrome (also called Trisomy 21) is a genetic condition caused by an error in the process that replicates and then divides up the pairs of chromosomes during cell division, resulting in the inheritance of an extra full or partial copy of chromosome 21 from a parent. This extra chromosomal DNA causes the intellectual disabilities and physical features characteristic of Down syndrome, which vary among individuals.
Duplication, as related to genomics, refers to a type of mutation in which one or more copies of a DNA segment (which can be as small as a few bases or as large as a major chromosomal region) is produced. Duplications occur in all organisms. For example, they are especially prominent in plants, although they can also cause genetic diseases in humans. Duplications have been an important mechanism in the evolution of the genomes of humans and other organisms.
Epigenetics (also sometimes called epigenomics) is a field of study focused on changes in DNA that do not involve alterations to the underlying sequence. The DNA letters and the proteins that interact with DNA can have chemical modifications that change the degrees to which genes are turned on and off. Certain epigenetic modifications may be passed on from parent cell to daughter cell during cell division or from one generation to the next. The collection of all epigenetic changes in a genome is called an epigenome.
A result indicating that the tested man is not the biological father.
Two separate eggs (ova) are fertilised by two separate sperm, resulting in fraternal or ‘dizygotic’ (two-cell) twins. These babies will be no more alike than siblings born at separate times. The babies can be either the same sex or different sexes.
A unique set of DNA markers used to identify an individual or establish biological relationships.
The genetic makeup of an individual, inherited from both parents.
A result showing a high probability that the tested man is the biological father.
A statistical value indicating the likelihood of paternity compared to random men in the population.
A paternity test conducted under strict chain of custody procedures for use in legal cases (e.g., child support, immigration).
A specific location on a chromosome where DNA markers are analyzed.
A change in a DNA sequence, which can sometimes affect test results and require further analysis.
A paternity test conducted without the mother’s DNA, relying solely on the child and alleged father’s DNA.
A test that determines paternity before birth using a sample of the mother’s blood, which contains fetal DNA.
The basic building block of DNA, consisting of adenine (A), thymine (T), cytosine (C), and guanine (G).
The percentage likelihood that a tested man is the biological father, typically 99.9% or higher for inclusion.
A method used to amplify DNA markers for testing.
The statistical probability that a man is the father, based on genetic comparison.
A test done at home using a DNA collection kit, but not legally admissible.
A DNA sample used for comparison in a paternity test (e.g., child’s DNA).
DNA testing to establish biological relationships beyond paternity (e.g., siblingship, grandparentage).
The Standards Council of Canada (SCC) is a Crown corporation established by an Act of Parliament in 1970 to foster and promote voluntary standardization in Canada. It is independent of government in its policies and operations, although it is financed partially by Parliamentary appropriation.
A type of genetic variation used in certain DNA tests.
Repeated sequences of DNA used in forensic and paternity testing.
A painless way to collect DNA by swabbing the cheek.
A test that examines the Y chromosome, passed from father to son, useful in cases where the alleged father is unavailable.
