DNA Tests

TNG V11 added the capability to track DNA Tests to its list of features.

16. DNA: A new Admin category has been added for DNA Tests. After a test is created, it may be linked to any number of people in the database. If a person is linked to any tests, those tests will be shown on the person's individual page.

See TNG and DNA Tests

Introduction

This is not a definitive article on DNA and the reader is encouraged to use the numerous available resources. A good starting point is the International Society of Genetic Genealogists – ISOGG. See the references below

The use of DNA to help with genealogy began in 2000 and is now called genetic genealogy. Using DNA for genealogical research requires that a test result be compared to other tests. It is important to understand this concept, as DNA test results, alone, will not give any information about any specific relative. It must be compared with other test results and then combined with traditional research to be useful.

DNA exists in (almost) every cell in your body. It exists in two places inside the cell – outside the nucleus and inside the nucleus. The extra-nuclear is the mitochondria, which provide the power for the cell. The nuclear DNA is what determines inherited traits and it consists of 23 pair of chromosomes or 46 chromosomes. The first 22 pairs are called autosomes. The 23^rd pair are the sex chromosomes – X and Y. A person possessing an X and a Y chromosome is male and a person possessing two X chromosomes is female. Each of the four types of DNA can be used in genealogical research.

DNA Testing

DNA testing can be used as a tool to discover and provide additional clues that can help with your family research. DNA testing of ordinary living people can provide near term and even ancient anthropological information about one's ancestors, not available in any other way. When used with more traditional research methods, DNA test results can scientifically help link and even sometimes prove or disprove relationships not otherwise available to anyone doing genealogical or historical family research.

There are several different types of DNA testing which can explore and help with different types of questions. Some tests concentrate on only the direct male lines, some on just the maternal lines and some in a more general relationship way. Combinations of various DNA test, especially within a specific family or group of related families can help explore and explain relationships which collectively can further one's knowledge and understanding of that family.

DNA tests themselves are done by separate specialty labs. Currently, TNG provides a way to record and track any and all of the many different types of DNA tests, in one place, by any and all of the individuals and families within your database.

Types of DNA Tests

There are four types of DNA which can be tested.

Autosomal DNA (atDNA)

atDNA is inherited from both parents, approximately half from each parent (i.e. it is recombinant). Sophisticated matching mechanisms are required to compare atDNA tests and the amount of autosomal DNA inherited from an ancestor diminishes exponentially with each preceding generation. It is useful in finding recent relatives out to the third and fourth generation and, occasionally, more distantly related. Progress is being made in identifying which parent contributed specific segments of one's DNA,though it may not be useful to most researchers.

One of the well-deserved criticisms levelled at atDNA is the assertion that it can identify one's ethnicity or geographic origins. This is due to several factors, e.g. (a) one loses the contribution from an ancestor every 7 to 10 generations; (b) the ethnicity predictions are based on studies of people groups who have survived but ancestors whose genetic information has been lost cannot be represented, and (c) it cannot be known for certain where any people group lived at any particular time. (Note that all the DNA tests provide ethnicity information. Y-DNA and mtDNA are more useful, albeit for a smaller subset of one's ancestors.)

mitochondrial DNA (mtDNA)

Everyone has mtDNA . Some characteristics which make it particularly interesting are (1) it exists outside the cell nucleus, (2) it exists in much greater quantities than any of the other types of DNA and (3) it is inherited only from one's mother. (Its greater quantity explains why DNA tests on ancient specimens can often only be done with mtDNA because decay has destroyed the other types.)

mtDNA is similar to Y-DNA in that it provides a signature (haplogroup) defining everyone related to you through your direct maternal, or matrilineal, ancestry. This means your mother, her mother, etc. It differs from Y-DNA in that it does not follow the matrilineal line of descent as might be expected. Each mother gives it to all her children, so both her son and her daughter get mtDNA from her, but only her daughter can pass it on to her children. The use of mtDNA is complicated by (1) a woman's surname change at each generation, (2) it mutates slowly, making it less effective at demarking recent branches of the family tree and (3) the mode of transmission, mother-to-children, can be confusing.

X-chromosome DNA (X-DNA)

The X-chromosome is part of the 23^rd pair of sex chromosomes. Everyone has an X-chromosome, but women have two and men only have one. Women therefore get one from each parent, while men only get theirs from their mother. As with the other types of tests, its method of transmission determines how it can be used in genealogy. It is currently the least used type of test probably because of that unusual method of transmission.

Y-chromosome DNA (Y-DNA)

Only males have Y-DNA . A Y-DNA test provides two distinct signatures which identify all your direct-male ancestors and their direct-male descendants. This direct-male relationship (both ancestral and descendant) is sometimes called patrilineal and it means father to father for ancestral and father to son for descendant. The names of the two signatures are haplogroup and haplotype (see below). These signatures will be identical to or very nearly the same as all your direct-male relatives. ]</ref>

DNA Projects

There can be value in joining a DNA Project for a person who has taken a DNA test. There are projects that address each type of DNA test. The most common type of project is the Surname Project. These will be for Y-chromosome tests. Mitochondrial DNA (mtDNA), like Y-DNA, highlights a specific line, in this case the matrilineal line, but the constantly changing married names of the women make it difficult to use. Also, its very slowly mutating characteristic makes it difficult to discern branches of the tree, so it is best suited for a Geographical DNA Project. There are also projects for haplogroups.

Some DNA Terminology

Autosomal DNA (atDNA)

Autosomal DNA (often abbreviated atDNA) is comprised of the first 22 pair of chromosomes, also known as the autosomes. A person gets approximately one-half of their atDNA from each parent. The contribution from each preceding generation is reduced by a factor of 2, 1/2 from each parent, 1/4 from each grandparent and so on.

Human DNA contains approximately three billion base pairs, which are inherited from your ancestors. Base pairs are the data used in atDNA and, at 32 generations back, one would have 4.3 billion ancestors, or more ancestors than you have base pairs, so it can be seen that it is impossible for anyone to have DNA from all their ancestors. Assuming 30 to 35 years per generation, this represents ancestors from approximately 1,000 years ago. This illustrates again why ethnicity predictions from autosomal tests should be taken as light-hearted factoids and not serious genealogy. An ethnicity report is based on population groups from tens of thousands of years ago and many of your ancestors will not be represented in your DNA.

Genealogically Useful Time Frame

This is important to the genetic genealogist as non-recombinant DNA tests (mtDNA and Y-DNA) point to ancient people groups. Recombinant DNA (atDNA & X-DNA) gets diffused over time and is better suited for recent relationships. A genealogically useful time frame is approximately when surnames appeared and for which documentation is available, or about 1,000 years ago. Anything beyond that can be very difficult to substantiate. (Surnames appeared in Europe approximately 1,000 years ago and were adopted in other places after that. Turkey didn't require surnames until 1934. Likewise, the availability of documentation varies over place and time.) Y-DNA STR tests, due to its higher mutation rates, and atDNA can effectively represent recent relationships.

Haplogroup

A haplogroup is a large group of people related to you as defined by a SNP which occurred in the mtDNA or Y-DNA of one of your ancestors. The overall family tree for humans is called a phylogenetic tree and each of its branches represents a more recent haplogroup. The most ancient mtDNA haplogroup known is "L". Everyone who has ever lived is believed to descend from mtDNA haplogroup L, making it the largest haplogroup. Conversely Y-haplogroup A encompasses every man who has ever lived. Most men in America belong to the much more recent haplogroup R which is thought to have appeared about 20,000 years ago. More recent haplogroups represent smaller subgroups of the human race. Scientists are discovering even more recent haplogroups, which will make DNA even more useful to the genealogist. Each haplogroup is defined by one or more SNPs and the most recent haplogroup is defined by what is called a terminal SNP. A terminal SNP will be redefined as more recent ones are discovered.

Haplotype

We use a narrow definition for haplotype for genealogical research. It is specific to Y-DNA and, simply put, it is a set of numbers that are unique to the individual who took the test – a "signature" for that person. Others who have similar or identical haplotypes are almost certainly related, though "genetic drift" can cause false positives with unrelated individuals who have similar haplotypes. The numbers are called "alleles" and represent the number of times a base pair is repeated. Whereas a haplogroup denotes a branch on the human tree, a haplotype belongs to one individual and those very closely related to him.

matrilineal

This term can mean different things. For this article, it means a line of females, unbroken by a male, both ancestors and their descendants. Mother to mother to mother, etc. and mother to daughter to daughter, etc.

Mitochondrial DNA (mtDNA)

Mitochondrial DNA is distinct from the other types of DNA. It is located outside the nucleus of the cell in the mitochondria. There is only one nucleus in a cell and only one set of nuclear DNA, but there can be thousands of mitochondria in a cell. Archaelogists studying the DNA of ancient specimens often find that there is little or no nuclear DNA remaining while some mtDNA may still remain. Everyone has mtDNA, and they all get it from their mother – but only women pass mtDNA to the next generation.

MRCA

This stands for "Most Recent Common Ancestor" and is the ancestor where the lines of two people intersect. The MRCA for first cousins is their grandfather or grandmother.

patrilineal

For this article, it means a line of males, unbroken by a female, both ancestors and their descendants. Father to father to father, etc. and father to son to son, etc.

recombinant and non-recombinant DNA

When the body produces an egg or a sperm cell, it must contain only one chromosome and not the pair found in the body, and they make the pair when they combine to form a new person. A woman's egg contains fragments from both her parents and a man's sperm cell contains fragments from both his parents. (This term can also refer to genetic engineering.)

The autosomes (autosomal DNA) recombine but the Y-chromosome and the mtDNA are passed directly from parent to child and do not recombine. Continuing to be a troublemaker, the X-chromosome recombines sometimes and not others – a woman gets one X from her father and a recombined one from her mother's two X-chromosomes. In all other cases, it is non-recombinant.

SNP SNP is an abbreviation of Single Nucleotide Polymorphism – and represents a change in a base pair on a chromosome (called a mutation). A SNP is used to define a branch in the phylogenetic tree (i.e. a haplogroup). It was once thought a SNP occurred only once in human history, but rare instances have been found of SNPs having occurred more than once and in more than one place on the phylogenetic tree. This complicates the study of SNPs and the definition of haplogroups. Another problem is that no one can know when a SNP occurred. It has to be predicted by, again, doing traditional genealogy and archeological research.

The term "terminal SNP" refers to the most recent SNP in your genome which has been accepted by geneticists as unique and meaningful. It defines the most recent and smallest haplogroup to which you belong. A terminal SNP will be redefined as more recent ones are discovered, moving your haplogroup designation closer to you in time.

STR

Short Tandem Repeat ... not a true change of the DNA, but a "stutter" where a portion is repeated. The STR is predicted to change once in 250 to 400 generations, so you test a whole lot of them to get resolution. These provide the "haplotype" for an individual and he can compare that with others to see if they are recently related. (In older texts, it is sometimes called "junk DNA" because it appeared to have no purpose or effect.)

Triangulation

A powerful tool is determining the haplotype of an ancestor. This is done through a process called Triangulation. It involves testing as many cousins descended from that ancestor and carefully working back up the pedigree tree to find where each difference (mutation) occurred. It is most commonly done with Y-STRs but can be used for other forms of DNA as well.

X-DNA

The X chromosome is part of the 23^rd pair of chromosomes, known as the sex chromosomes because they determine the sex of an individual. Men have one X chromosome and women have two. Its method of transmission can be confusing and difficult to analyze. A man get his single X-chromosome from his mother and a woman receives one X-chromosome from her father and a recombined one (representing her maternal grandparents) from her mother.

Y-DNA

The Y chromosome is part of the 23^rd pair of chromosomes, known as the sex chromosomes because they determine the sex of an individual. Only males have a Y chromosome and it therefore provides a tool to identify men who are related patrilineally.

Recommended Readings

If you want to learn more about DNA Testing, the following may be helpful:

List of DNA testing companies

Choosing a DNA testing company

ISOGG Autosomal DNA testing comparison chart

DNA Testing for Genealogy Part 1 - Y-DNA

DNA Testing for Genealogy Part 2 - mtDNA

DNA Testing for Genealogy Part 3 - autosomal DNA

DNA Testing for Genealogy Part 4 - ethnicity percentage

Family Tree DNA Interpering Genetic Genealogy Results

Genetics Glossary

Gedmatch: a DNA geek’s dream site

ISOGG Haplogroup

World Families Net definition of haplogroups

DNA Explained What is a haplogroup

23andMe More about haplogroups

Charles Kerchner's YDNA Haplogroup Descriptions & Information Links

Charles Kerchner's MtDNA Haplogroup Descriptions & Information Links