Paternity Testing Glossary

The terms and definitions involved with DNA testing can often be confusing. Our DNA paternity glossary will help to explain the DNA testing process.

A
Accreditation: is a series of steps in which a business is reviewed to make sure it is functioning either on par with or above the standards set by certain respected organizations, governing bodies and/or an industry as a whole. An organization may seek and receive accreditation from different bodies.

Alleles: are gene variations, therefore different forms of the same gene found in pairs, with pairs occupying various locations on chromosomes. Alleles can be thought of as genetic toggle switches which work to determine characteristics like eye color, hair color, height, facial features, etc. Alleles are used as genetic markers in DNA testing for paternity or maternity.

Amelogenin
: is a marker that is different in females and males, and makes up one of the genetic markers utilized in DNA testing to help determine paternity.

Amniotic Fluid: is the liquid surrounding a baby in the mother’s amnion, or amniotic sac, during its development. Though the primary function of amniotic fluid is to protect the baby, it contains concentrated amounts of genetic material and is therefore very useful in determining information about the baby pre-birth, including gender and paternity (in prenatal paternity testing). Often some of this fluid is drawn from the mother prior to birth in a procedure called amniocentesis to check the health of the baby.

Ancestral: refers to something inherited from a person’s ancestors (parents, grandparents, great–grandparents, etc.). In genetic terms, it refers to characteristics passed down through a bloodline. These characteristics can manifest themselves in physical appearance, as well as in predispositions to certain mental and physical health related issues. Ancestral DNA testing can be useful in determining a person’s genetic heritage.

Anthropology: is the study of humans and their history. It tends to walk side by side with archaeology, the study of human cultures, and the two are often confused. One of anthropology’s base goals is to pinpoint defining characteristics of races at different points throughout history to help better understand humanity, its timelines and geographical migrations, and its physical evolution. Anthropology relies greatly on the study of genetics to help it achieve this goal.

Antigens: are substances that cause a person’s immune system to react, either mildly or severely. A person’s system will detects antigens as foreign matter and try to eliminate them through the production of antibodies (which help neutralize antigens). Some antigens and antibodies can be inherited from either parent or both, and their presence may be used to determine vital information about body systems. One such example is blood typing, which looks for certain antigens on the surface of red blood cells.

Avuncular: refers to the scientific study of the origins, behaviors, and the physical, social, and cultural development of humans.

B

Base pairs: (BP) refers to the rung portion of the ladder structure of a DNA strand, the horizontal bars in the middle that connect the outside two vertical helix bars. Base pairs are constructed of nitrogenous bases – adenosine, thymine, cytosine or guanine – held together in the middle with loose hydrogen bonds. Adenosine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). The number of these base pairs in a strand of DNA determines the strand’s size, which can be useful in genetic testing, including DNA testing for paternity.

Biological: as a word, is used to differentiate a physical “blood” relationship from one based in emotional bonds. For example, in the case of adoption, a child’s birth parents are referred to as the biological parents, ones from which the child has inherited his or her DNA and genetic characteristics. DNA tests are employed to identify biological relationships between people.

Blood typing: Human blood is typed as either A, B, AB, or O, according to whether the red blood cells show the presence of certain antibodies. This classification system also includes a positive (+) or negative (–) suffix, dependent on whether the person’s blood has the Rh D antigen present. Both parents contribute to their offspring’s blood type, and so it is possible for a mother to have a different blood type than the child she carries. Blood type can be quickly determined by a simple blood sample test.

Buccal swab: The word buccal refers to a person’s cheek, and buccal swabbing simply means to rub the inside of the mouth in the cheek area to collect loose cells for analysis. The collection device, or swab, generally looks like a large Q–Tip. Buccal swabbing is a common method for collecting DNA for analysis and determining paternity or other biological relationships.
C
Chromosome: can be thought of as the body’s gene cataloging system. There are 23 pairs of chromosomes in each cell in our bodies (for a total of 46 chromosomes in each cell), and each chromosome is made up of proteins and long strands of gene–carrying DNA. We receive 23 chromosomes from our fathers and 23 from our mothers. The 23rd pair of chromosomes determines gender, either labeled as XX for females or XY for males (named so after the actual shape these chromosomes take). Before a cell divides into two new cells, the chromosomes duplicate themselves so that they can deliver DNA to each new cell being formed.
D

DNA
: stands for deoxyribonucleic acid, and DNA makes up the bulk of our chromosomes. DNA is often referred to as acting like the body’s blueprint or set of cellular instructions. Each strand of DNA looks like a twisted ladder, or “double helix.” Base pairs of adenosine, thymine, cytosine and guanine make up the rungs of the ladder, and the number of base pairs determines the length of each DNA strand. DNA can be found in a cell’s nucleus (nuclear DNA), and in smaller amounts in a cell’s mitochondria (mitochondrial DNA, or mtDNA). While each person’s nuclear DNA is composed of information half of which is inherited from the mother and half from the father, all mitochondrial DNA in humans (both in males and females) is inherited from the mother. DNA can be used by scientists to help determine parentage, as well as a wide range of other information about the source of the DNA. Mitochondrial DNA is particularly useful in making determinations about maternal or female bloodlines.
F
Fraternal twins: Normally, there is only one egg available in the womb at any given time ready for fertilization. If there are two or more eggs present and they are fertilized, the result is fraternal twins (or triplets, etc.). Because the eggs are fertilized by different sperm, each resulting child’s DNA will be different, and thus their genetic blueprints will be different. They may look very different physically, sound different, act different and have different health issues. Fraternal siblings may even be different genders. Fraternal twins will likely share some similar characteristics, however, as they have both inherited DNA from the same parents. The likelihood of having fraternal twins is determined entirely through the mother and factors affecting her reproductive system. A twin zygosity test can determine whether siblings are identical or fraternal twins.
G

Genes
: are the basic units that determine on the cellular level what characteristics we inherit from our parents and how our bodies will form. Genes are often referred to as containing “coding” or instructions for how their containing cells are supposed to function and what traits they will exhibit. Genes are inherited from both parents.

Genealogy
: is the practice of tracing a person’s or a family’s line of descent. Genealogy has many tools at its disposal including written accounts (such as birth, marriage, tax and death records), spoken accounts (stories passed down through generations) and genetic testing results. Depending on the amount and reliability of the information available, a person’s genealogy may be charted back by only a few generations or by many generations spanning centuries. DNA ancestry testing can help trace a person’s genealogy.

Genetic markers: are points of variation in DNA that scientists can use to decode and interpret information about the source of the DNA. These markers act as genetic “bookmarks,” allowing scientists to quickly determine genetic characteristics associated with the marker’s location (locus) on the DNA strand. There are 16 genetic markers GTL commonly uses in determining parentage: amelogenin, CSF1PO, D13S317, D16S539, D18S51, D21S11, D3S1358, D5S818, D7S820, D8S1179, FGA, PENTA_D, PENTA_E, TH01, TPOX and VWA.

Genome: does not refer to a specific organism but to a person’s entire genetic blueprint, which is to say the collective of its DNA’s instructions. A genome is the complete set of instructions needed by the body to create that individual. Every cell that contains a nucleus also contains a complete copy of that individual’s genome. While the study of genetics looks at individual genes or gene groups that make up a genome, the study of genomics looks at the genome as a whole.

Geogenetics: refers to the process of drawing correlations between an individual and different distinct groups of people located throughout the world. Comparisons are made between the genetic characteristics of an individual and the genetic characteristics of various groups to help determine possibilities in geographical migration and ethnic descent. Ancestral DNA tests can be used to discover geogenetic links.

Grandparentage Test: is a genetic test similar to a parentage test that allows a scientist to discover whether one sample donor could be a biological grandparent of another sample donor. This sort of test can be quite valuable in helping uncover predispositions to health problems.

H

Heterozygous: is a term for describing a gene pair site (locus) that holds two different genes governing a single trait (such as eye color), one provided from each parent. For example, if a brown eye gene is provided by the mother and a blue eye gene is provided by the father, the locus determining the child’s eye color would be considered heterozygous.

Homozygous: refers to a gene pair site (locus) holding two identical or very similar genes governing a trait, one provided from each parent. For example, if a blue eye gene is provided from the mother and a blue eye gene is provided from the father, the locus determining the child’s eye color would be considered homozygous.
I

Identical twins
: If only one egg is fertilized and it develops into two or more embryos, the result is a set of identical twins (or triplets, etc.). Because there is only one egg and one sperm involved, the twins will share virtually identical DNA. They will look the same and will be the same gender. The chance of producing identical twins is random, current research having proven no influence on the possibility by either the mother or the father’s genetic makeup.

Immigration: is the act of entering a new country to settle permanently.

Indigenous: as a term, refers to an origin. If a group of people are found to be original inhabitants of a geographical location, those people are considered indigenous to that area. Indigenous peoples of a certain region will likely share some physical characteristics, as well as a common written or oral history and other cultural identifiers that make them unique. The term can also refer to plants, animals or minerals found originally in an area as well.

Infidelity: is another term for unfaithfulness to a sexual partner, especially a spouse.

ISO 17025: is a specific ISO standard that offers guidelines for laboratories that conduct calibration and testing, such as paternity and forensics sampling. The standard (first written in 2001 and revised in 2005) outlines guidelines for both management and technical requirements, and quality management is considered one of the highest priorities of the standard. Laboratories meeting the ISO 17025 standard are considered highly competent and efficient.

ISO: stands for International Organization for Standardization. ISO is an organization that outlines acceptable standards and levels of operation and industry (including guidelines for health, safety and environmental conformity) for many sectors, including scientific sampling. This international standardization and recognition allows businesses working under ISO standards to all start from a level playing field, so to speak. Competition, then, results from how far companies exceed ISO standards, raising the overall quality of goods and services provided within an industry. While ISO is not a governmental organization, many of its standards are (or become) the basis for laws, so its influence upon industry is significant. Many accrediting bodies use ISO standards as the bases for awarding accreditation.
L
Locus: Loci (the plural of locus) are the points along chromosomes where specific alleles are located. Genetic mapping is possible through cataloging the loci in a genome and the genetic traits determined at those points.
M

Maternity test
: Maternal refers to mother. A maternity test uses DNA testing to determine whether or not it is possible a woman is the biological mother of a particular child.

Midwifery: refers to the techniques of a midwife, a woman skilled in aiding the delivery of babies.

Mitochondrial DNA: Mitochondria are often referred to as cellular power supplies or batteries, as the primary function of mitochondria is to regulate cellular energy functions. Mitochondria contain DNA, and mitochondrial DNA has its own genome, unique from the cell’s nuclear DNA genome. All mitochondrial DNA in humans (both male and female) is inherited from the mother. Mitochondrial DNA is particularly useful in making determinations about maternal or female bloodlines.
N
Nuclear DNA: can be found in a cell’s nucleus. A person’s nuclear DNA is composed of information inherited half from the mother and half from the father, and helps to create that individual’s genome, or set of genetic instructions. DNA can be used by scientists to help determine parentage, as well as a wide range of other information about the source of the DNA.

Nucleotides: are the building units of both DNA and RNA, composed of a nitrogenous base, a sugar and a phosphate.
P
Paternity test: Paternal refers to father, and a paternity test is used to determine the possibility of whether or not a particular man could be the biological father of a certain child. In the past, common methods of paternity testing included blood typing, analyzing certain proteins and looking at human leukocyte antigens (HLAs). Currently, the most certain method of testing is through DNA analysis, which relies on polymerase chain reaction (PCR).

PCR: stands for polymerase chain reaction, a way of amplifying DNA so that unlimited copies may be produced from the original DNA sample. The technique employs DNA polymerase, an enzyme which helps to facilitate the replication of DNA to carry over genetic information to new cells as a cell divides and multiplies. This method of reproducing DNA in a laboratory is both a fast and efficient way to ensure there is ample DNA for analysis.

Power of Exclusion: refers to the ability of a genetic test to exclude a man from the possibility of biological paternity. Power of exclusion is dependent upon the genetics of both the mother and child, and upon the ethnic backgrounds of the mother and alleged father.

Prenatal: as a term, refers to developments prior to birth. This term can be used to describe events occurring while the fetus is still in the womb, and affecting either the mother or the child, or both. DNA can be retrieved prenatally from a child via an amniocentesis test.
S
Serology: is the study that deals specifically with the identification of antibodies in bodily fluids, most often in blood serum but sometimes in other body fluids like semen, urine or saliva. Serology can be useful in helping to identify genetic characteristics in samples of unknown origin.

Siblingship test: is a DNA test used to determine whether or not two people could be siblings. Siblingship tests can be very useful in parentage cases in which one or both parents is either unavailable or deceased.

SNP: stands for single nucleotide polymorphism, which is the case of a nucleotide in a strand of DNA differing from what is expected at that location (locus). In humans, looking at these variations can help doctors to determine how a person’s system might react to certain medications or to certain illnesses. This can be useful in personalizing medical treatment.

STR
: stands for short tandem repeat, which is a particular pattern DNA analysts look for in cataloging differences in DNA profiles. STRs are patterns in which several base pairs are repeated in sequences along a strand of DNA, each person’s genetic material exhibiting unique patterning.
T

Twin Zygosity test
: is used to determine whether twins are identical or fraternal. The term “zygosity” refers to whether DNA is similar or different between two fertilized eggs (or zygotes). Homozygosity (developing from a single egg) results in identical twins. Heterozygosity (developing from separate eggs) results in fraternal twins.
X

X–SV test
: looks at mitochondrial DNA (mtDNA) in order to determine whether or not two people or a group of people could be related through maternal bloodlines.
Y
Y–STR test: looks at STRs on the Y chromosome in order to determine whether or not two males could be related through paternal bloodlines.

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