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DNA Genealogy |
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Genetic genealogy is considered by many as an exciting new genealogical tool. Many ethnic and surname genetic studies have been published in the literature or on the web and some invite your participation. The National Geographic Magazine's Genographic project is attempting to determine the migratory paths of ancient peoples as they colonized the planet Earth. Many labs are now specializing in this branch of genomics and the price for individual tests is steadily going down. On this page we will give a very brief introduction to this exciting new field and describe our own experiences. What is DNA?The following is a superficial explanation of this complex scientific field. For more details, we encourage you to read the following relevant chapters in the free encyclopedia Wikipedia: DNA is the abbreviation for Deoxyribonucleic Acid, a very large "macro molecule" that contains all the necessary information to reproduce any living organism. DNA is packaged in several large molecules called chromosomes. A chromosome consists of a helical structure consisting of two intertwined complementary DNA strands. Each DNA strand consists of a twisted "backbone" to which are attached sequences of four nucleotide bases, abbreviated as A, C, G and T. It is the particular sequence of these bases that contains the genetic information (think of it as defined by a very large base-4 number). In humans, the number of chromosomes is 46 and the number of bases is estimated to be 3x10^9 or about 3,000 million. Two of the chromosomes determine the sex of the individual, females have two X chromosomes and males have one X and one Y chromosome. Sections of the DNA strands that are active are called "genes". Genes are the fundamental unit of heredity in an organism. The number of genes in a human is still uncertain but is usually estimated at approximately 20,000 to 25,000 (for a discussion of the results obtained by various studies and the reasons for uncertainties visit How Many Genes?). The Human Genome Project completed the identification of the human genome in 2003, although much research remains to be done, particularly on determining the functions of the various genes. DNA genealogy concentrates on analyzing particular sections of the remainder or inactive DNA, sometimes called "junk DNA". It should be emphasized that commercial DNA genealogy tests do NOT determine paternity or susceptibility to inherited diseases.
Paternal and maternal lineagesThe two most common types of genetic genealogy tests are the Y chromosome or Y-DNA (paternal line) and the mitochondrial or mtDNA (maternal line) tests. The object of the tests are to compare one individual to another to determine the numerical probability that the two individuals are related within a certain number of generations. Paternal lineajeThe Y- chromosome DNA is passed from one generation to the next only from male to male. Since surnames are also usually passed from one generation to the next from male to male, this test is best suited for comparing individuals with the same surname, or at least with suspected common parentage. Because the Y-DNA is passed only from male to male, only a relatively small number of your ancestors, and their male offspring, share your Y-DNA, essentially only those also sharing your surname. Your male descendants also share your Y-DNA, but only if you are a male.
Maternal lineajeThe maternal, or mtDNA is passed from a female to all her offspring, male and female. The mtDNA, however is only passed to the next generation by the female. Again, there are only a small number of your ancestors, and their female offspring, that share your mtDNA. Your male and female descendants also share your mtDNA, but only if you are female. Your male descendants cannot pass your mtDNA to any of their descendants.
HaplogroupsHaplogroups are DNA test results which correspond to an ethno-geographic group. Thus it can be considered as the DNA equivalent of a "tribe". The haplogroup is generally associated with the migratory path of ancient peoples (anthropologists believe that all of us descend from distant ancestors who evolved about 200,000 years ago in the highlands of East Africa). A Y-DNA or mtDNA test will usually result in a haplogroup prediction. Some companies offer more detailed tests to determine the sub-haplogroup within a main haplogroup. In addition some companies offer tests to determine the percentage of each major ethnic group present in an individual. as well as determining the presence of markers for particular ethnic origin (see the Wikipedia article on Genealogical DNA test for a listing). Some of these tests are still considered controversial.
How are the tests done?Generally, you order a test kit from one of the testing organizations (see below) The typical testing kit consists of enough materials to obtain two samples. Each sample is obtained by scraping the inside of the cheek with a small stiff brush for a full minute. The tip of the brush is then placed inside a specimen vial and the button at the back of the brush handle is pushed to drop the brush part into the solution in the sample vial. The vial is then closed securely. The second sample is obtained in the same manner after waiting at least 8 hours. Both vials, which are tagged with a unique identifying number, are then mailed back to the lab. Processing of the sample usually takes about 8 weeks. The Sorenson Molecular Genealogy Foundation (see the list of genetic testing laboratories below) gets the samples by means of a special mouthwash, without the need for any scraping with a brush. What results do you get back?Results vary depending on the test(s) you have ordered. Y-DNAY-DNA tests can only be performed on a male individual. Females can choose a male relative with the same (unmarried) surname for this test. In the case of the simplest paternal line Y-12 test, what you get back are the numerical results at 12 Y-DNA marker locations. The numbers indicate the times that a particular sequence of bases repeats at each of the marker locations. The marker locations and nomenclature ("Aleles") have been standardized among different labs so that results can be compared worldwide. These repeats are referred to as "Short Tandem Repeats" or "STRs". In general, these marker locations have been found to mutate frequently (in terms of tens of thousands of years) so they serve to differentiate genetic lines and to establish migratory routes. You can then visit one of the searchable Y-DNA databases, to see if any other individuals match your particular number of repeats for each Alele. Usually you will find a few that do match. If they do not share your surname, however, it is unlikely (but not impossible) that the individual is related. On the other hand, if one of the surnames matches yours, it is quite likely that he is related. On the web you can find the numerical probability of two individuals being related if they match exactly or even if they differ slightly in one or more of the repeat values. The certainty goes up significantly if more Aleles are tested. Most labs can make additional tests on the same sample, at additional cost, to bring the number of Aleles tested from 12 to 25, 37 or 59. These tests can be ordered at a later time to help resolve whether two individuals with the same Y-12 markers are related (of course both individuals must have the additional Aleles tested for the comparison to be made). mtDNAmtDNA tests can be performed on both male or female individuals. In the case of the simplest mtDNA test, tests are done on the HVR-1 (hyper-variable 1) region of the DNA. The results indicate the location and how the individual's mtDNA differs from that of a reference sequence, the Cambridge Reference Sequence (CRS), which is the accepted mtDNA standard sequence. Usually the comparison is made in a 569-base portion of the CRS. You can then visit one of the searchable mtDNA databases to see if any other individuals match your mtDNA mutations. Since any matching individuals are unlikely to share your maternal surname, any further research has to be done by contacting the individual in question and sharing your maternal genealogy data to look for a common female ancestor. If you do find a match, you can also expand (at extra cost) your mtDNA testing to also include a second region of the CRS, the HVR-2 region to further refine your results (of course, both individuals must be tested for the HVR-2 region for a comparison to be made). HaplogroupFor both Y-DNA and mtDNA, the lab results will also include your "haplogroup". The haplogroups correlates your test results to the closest geographic group sharing the same genetic markers and indicates the most likely ethnic group and migratory path of your ancestors. Some labs can do additional tests (at additional cost) to further refine the haplogroup subgroup and attempt to refine the ethnic group and geographic location. My own ExperienceMy reasons for doing genealogical DNA testing were several. On the one hand, there was an element of scientific curiosity to see if the migratory routes of my ancestors agreed with my researched genealogical data. Also there was a desire to determine if any other individuals with my surname in the new world shared a common ancestor. In particular, I was looking for descendants of one Julian Saturnino Elizondo Beraza, brother of my great-grandfather who family legend said that had emigrated to the New World. The Y-DNA haplogroup results, not surprisingly, indicated that my branch of the Elizondo's indeed had migrated to Europe (my Y-DNA haplogroup R1b1 is the most common in European populations). Disappointingly, I did not find in the public Y-search database any other Elizondo's that matched. I did find several individuals that matched my Y-DNA-12 results, but with Irish or british surnames, not likely to be related. It is interesting to note that of the 45 DNA-Y results posted by members of the Cuban DNA project, 23 of them share this R1b1 haplotype, which is the most common among the members. The mt-DNA haplogroup results were a complete surprise. The test results indicated that I descended on my maternal line from Siberian Eskimos who migrated across the Aleutian chain and Alaska and down to North and South America*. This contrasted with my genealogy research which showed that my oldest known female ancestor, Maria Obregon Ceballos, was born in the city of Trinidad, one of the oldest towns in Cuba -founded in 1514, presumably of Spanish ancestry. My tentative explanation is that, probably in the early days of colonization, an ancestor in my maternal lineage married a native amerind female (a common practice in those days for Spaniards due to the shortage of female Spanish colonists and also a desire to own lands in the New World by marrying into a Cacique's family). The real story will probably never be known, at least until we can research parish records in the town of Trinidad. As you know, in our culture it is extremely difficult to trace a lineage on the female side because a female inherits her surname from the father and thus female descendants have different surnames every generation. It's interesting to note that of the 34 mtDNA results posted by members of the Cuban DNA project, 10 of them share this haplogroup A, which is the most common among the members.
Genetic testing laboratories
NOTES:
Genetic Data BasesHere are links to the searchable data bases which list individuals who have given permission to the testing laboratory to post their DNA test results:
Other hispanic regional DNA projectsThe following hispanic geographic DNA projects are also hosted by Family Tree DNA (FTDNA). Through these links you can review the test results of the members that have given their consent to publish results. Please note that, when you open an accoutn with FTDNA, you can only join one geographic project plus one surname project - we recommend that you join the Cuba DNA Project):
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DNA Genealogy - Updated
15-Jul-2007
Copyright © 2007-2013 - Ed Elizondo
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