Cambios

See [[TNG and DNA Tests]]

See [[TNG and DNA Tests]]

== DNA Testing ==

== DNA Testing ==

DNA testing can be used as a tool to discover and provide more clues and data 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.  

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.

''' Autosomal DNA (atDNA) '''

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.  

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. <em>Progress is being made in identifying which parent contributed specific segments of one's DNA,though it may not be useful to most researchers.</em>

See [[TNG and DNA Tests]]

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. <em>(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.)</em>

== Types of DNA Tests ==

 

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. <em>(Its greater quantity explains why DNA tests on ancient specimens can often only be done with mtDNA because decay has destroyed the other types.)</em>

 

 

''' X-chromosome DNA (X-DNA) '''

=== Y-chromosome DNA (Y-DNA) ===

The X-chromosome is part of the 23rd 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.

The Y-DNA test follows your direct paternal lineage that is it follows your father’s paternal ancestry. This line consists entirely of men. Your Y-chromosome DNA (Y-DNA) can trace your father, his father, his father’s father, and so forth. It offers a clear path from you to a known, or likely, direct paternal ancestor.<ref>[http://isogg.org/w/index.php?title=Y_chromosome_DNA_test&oldid=4956 ISOGG Wiki (http://www.isogg.org/wiki), Y chromosome DNA tests]</ref>

''' Y-chromosome DNA (Y-DNA) '''

=== mitochondrial DNA (mtDNA) ===

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.

The mitochondrial DNA (mtDNA) test follows your direct maternal lineage that is your mother’s maternal ancestry. This line consists entirely of women, although both men and women have their mother’s mitochondrial DNA (mtDNA). This means that fathers do not pass on their mtDNA to their children. Your mtDNA can trace your mother, her mother, her mother’s mother, and so forth and offers a clear path from you to a known or likely direct maternal ancestor.

[http://isogg.org/wiki/List_of_DNA_testing_companies List of DNA testing companies]

=== Autosomal DNA (atDNA) ===

<a href="http://isogg.org/wiki/Choosing_a_DNA_testing_company Choosing a DNA testing company]

Family TreeDNA's Family Finder test focuses on autosomal DNA, which is inherited from both your mother and your father, your four grandparents, your eight great-grandparents, etc. This test is designed to find living relatives on all of your ancestral lines within the last five generations and can also give you a breakdown of your ethnic makeup by percentage. This test cannot distinguish between matches from your mother’s side versus your father’s side.

== Some DNA Terminology ==

An X-chromosome DNA test looks at markers on your X-chromosome(s). Males have one X-chromosome that they inherit exclusively from their mother, and females have two X-chromosomes that they inherit from both parents, one from their father and one from their mother. This creates a unique inheritance pattern that while challenging to follow may provide many insights into one’s maternal heritage.<ref>[https://www.familytreedna.com/learn/test-types/x-chromosome-x-dna-str-testing-will-learn/ FTDNA What is X-DNA]</ref>

''' Autosomal DNA (atDNA) '''

== Vendors Selling DNA Text Kits ==

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.

[https://www.familytreedna.com/ Family Tree DNA]

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.

[http://dna.ancestry.com/ AncestryDNA]

This is important to the genetic genealogist as all DNA tests, with the exception of atDNA, represent ancient people groups. 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. <em>(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.)</em> Y-DNA and atDNA can effectively represent recent relationships.

[https://www.britainsdna.com/ Chromo2] [http://www.cymrudnawales.com/ Chromo2 Wales site] [http://www.irelandsdna.com/ Chromo2 Ireland site] [http://www.scotlandsdna.com/ Chromo2 Scotland site]

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.

For a comparison of Autosomal DNA test see [http://isogg.org/wiki/Autosomal_DNA_testing_comparison_chart ISOGG Autosomal DNA testing comparison chart]

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 &ndash; 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.

== Some DNA Terminology ==

 

 

''' Mitochondrial DNA (mtDNA) '''

 

 

The following terminology is used:

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.

'''autosome'''

''' 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.

:is a term used in genetic genealogy to describe DNA which is inherited from the autosomal chromosomes. <ref name=autosomal></ref><br />

'''Haplogroup'''  

''' recombinant and non-recombinant DNA '''

:Think of a haplogroup as an ancestral clan, a large family, like the Celts, or Vikings. These would be larger than Native American tribes, encompassing members of many tribes.  There are two male Native American haplogroups that include all Native American males. There are a few more African clans, or haplogroups, but not many.

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. <em>(This term can also refer to genetic engineering.)</em>

:Note: Though maternal and paternal haplogroups may have similar naming systems, their definitions are different.

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 &ndash; 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.

'''Mitochondria'''  

''' SNP '''

:are small organelles that lie in the cytoplasm of eukaryotic cells, such as those of humans. Their primary purpose is to provide energy to the cell. Mitochondria are thought to be the vestigial remains of symbiotic bacteria that were once free living. One indication that mitochondria were once free living is that they contain a relatively small circular segment of DNA, called mitochondrial DNA (mtDNA).<ref>[http://isogg.org/w/index.php?title=Mitochondrial_DNA&oldid=2938  ISOGG Wiki (http://www.isogg.org/wiki), Mitochondrial DNA]</ref><br />

SNP is an abbreviation of Single Nucleotide Polymorphism &ndash; 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.

:There are also clans for '''mitochondrial DNA''', tested by the mtDNA tests at Family Tree DNA, which follows the direct maternal line up your family tree.  This means your mother, her mother, her mother, etc.  Woman give their mitochondrial DNA to all of their offspring, males and females, but only females pass it on.

''' 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. <em>(In older texts, it is sometimes called "junk DNA" because it appeared to have no purpose or effect.)</em>

:Single Nucleotide Polymorphism ... a change in a base pair on the chromosome. These happen so seldom as to define a branch on the family tree. A major problem is that no one can know when a SNP occurred.  It has to be predicted by, again, doing traditional genealogy and archeological research.

'''STR'''  

''' X-DNA '''

'''Y-DNA'''

''' Y-DNA '''

:There are clans for the Y chromosome, which is of course tested by the Y DNA test at Family Tree DNA and generally follows the paternal surname up and down the tree. '''Y DNA''' is passed from father to son, only, through the Y chromosome which only males possess.

The Y chromosome is part of the 23rd 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 ==

== Recommended Readings ==