23 October 2008

Autosomal DNA (atDNA)

Many people are seeking to determine their ancestor whom they have been told descended from a Native American or an African American. There are family stories that a great-great grandmother or grandfather was a slave or perhaps a member of the Cherokee nation. Often these connections are difficult to prove with genealogical research.

Some companies provide information on your ethnic background by testing your autosomal markers and giving you a percentage of what culture those markers contain. To understand the usefulness and accuracy of this, one needs to understand autosomal markers.

Autosomal markers are distributed throughout all your chromosomes, and they represent your accumulated inheritance from your ancestors. That is, you inherent approximately fifty percent of your genes from your mother and the remainder from your father. In turn, each of them inherited about fifty percent from their parents. Those genes contain markers which are autosomal and which recombine or restructure themselves differently for every person at conception. In other words, these are the markers which make you look like your family, but not exactly…unless you have an identical twin. These markers make you a unique individual. They give you your mother’s high cheek bones, your father’s nose, etc.

Also, autosomal markers contain all your health issues. Science knows the markers for a few inherited diseases and progress toward knowing more is continuing. Health issues are believed to be a combination of marker mutations, making their jobs a bit more difficult. Scientists know that environment is the biggest factor for health issues, however. Granted, there are inherited diseases which raise the likelihood of someone’s health being hampered, but there is no guarantee it will in most cases. What we eat, what we breathe, and what we do after we eat (i.e., no exercise) are major factors contributing to our health, as well.

Autosomal markers are best used to help determine paternity and for use in forensics (See my blog on CODIS).

atDNA and Genealogy

Some testing companies give a percentage for various ethnic groups and claim to assign a tribe to African or Native American Heritage. The test result from these companies is displayed as percentages for various ethnic groups. Not every ethnic group can be determined. Basically, a tester would get a percentage for Western European, Native American, African, and Asian. For example, a person’s test could result in 36% Western European, 24% African, etc.

A genealogist would have to ask how helpful a percentage of a cultural group is to the search for ancestors. Some genealogists suspect that a particular ethnic group is part of their heritage, and they are comfortable knowing their DNA confirms this. Others find that just knowing that fact does not really advance their search for their family. Depending upon the researcher’s goals, this type of test may be very useful or not. A researcher needs to determine his or her reason for testing the autosomal markers and whether that result will fit his or her genealogical needs.

As each person inherits a unique combination from the parents, your test could you 15% Native American where your sibling might test and show 21%, or none at all. Remember, autosomal markers recombine differently with every conception.

Another issue is that those percentages will change as the company’s particular database becomes larger. That is, if you test today and again in five years, your percentages may change. For some, as I previously stated, it may be important for them to know what ethnic groups are in their background, although not all ethnic groups can be determined even by companies who test autosomal markers.

DNA does not recognize nationalities and tribes, per se. These are man-made terms. Scientists declare autosomal testing an “an infant science.” They feel the database which determines to what “tribe” someone belongs is too small. Tens of thousands of testers are needed to make genetic determinations. As the work on this continues, someday we may be able to correctly categorize with more accuracy, but given the lack of stable reliability of autosomal markers over time, there is concern that may not happen.

Accurate Testing for Native American or African DNA

The ONLY testing that can positively identify Native American or African ancestry is the Y-chromosome and mitochondrial DNA testing. This is due to the stability of the markers used for these tests to determine the haplogroup (your twig on the World Family Tree) for the basic ethnic groups. Testing particular parts of the Y-chromosome and the mitochondrial markers are reliable as they are consistent over time. That is to say, they rarely mutate, and those minor mutations help geneticists and genetic genealogists group testers into families. Geneticists have determined which twigs on the World Family Tree (Phylogenetic Tree) do tend to have Western European, Asian, Native American and African DNA; therefore, by testing either the all male line (Ydna test) or the all female line (mtDNA test) an accurate determination of these cultural groups can be made.

Unfortunately, these two tests only test the upper line of a pedigree chart (all male) and the bottom line of a pedigree chart (all female). This leaves everyone in the middle of that pedigree chart not able to test without a surrogate. Unfortunately, most of those researchers seeking to determine if they have a particular culture in their background would most often need to test those lines in the middle. So often the ancestor would be the great-great grandmother of the father’s father, etc. When the line is not all male or not all female, one must find another person to test for the targeted ancestor. To do so, follow these steps:

1. Put the ancestor you suspect to be Native American, African, etc. as number one on a pedigree chart.

2. If this ancestor is male, you can test either the top line of the chart (all male) or the bottom line of the chart (all female). If the ancestor who is now number one is a female, you can only test the bottom line of the chart. Remember: Females do not have a Y-chromosome and mother gives all her children the mitochondrial she has. However, only females can pass it to the next generation.

3. Bring the lineage forward to the present on either an all male or all female line for the male who is now number one on your chart or the all female line for the female who is now number one. This is called “Reverse Genealogy,” as normally a genealogist starts with his or herself and works backwards. You must now work forward to the present until you find a living person on that all male or all female line. Granted, this is a person you may not know. In that case, read my blog on convincing strangers to test.

..........If you find you cannot bring the line you need to the present, then you step back one more generation, if possible, and bring those needed lines to the present.

..........This may not be an easy task, but it has been done many times with great success.

In summary

As scientist, Roberta E. stated: “Clearly understand that the tribes information (as well as any other autosomal analysis information of this type) should be chocked up to the ‘interesting’ category, and little more until the underlying data bases and technology becomes significantly more robust.”

©Aulicino, 23 Oct 2008

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