Genealogy and DNA Testing

What is DNA?
Your DNA was derived from your mother and father, and theirs was derived from their mothers and fathers, and so on. Five generations represents 32 direct ancestors or approximately 125 years. Twenty generations represents 1,048,576 direct ancestors! You can find out your ancestors genealogy through DNA testing.

DNA is passed down from generation to generation. It is made up of four nucleotides: adenine, cytosine, thymine, and guanine. The order of these letters, A-C-T-G, makes up the DNA sequence.

Chromosomes are the package for DNA and genes. We each have 23 pairs of chromosomes. 22 are autosomes. The 23rd pair is the sex chromosome. The 23rd chromosome from the mother is always an X. A child inherits either an X or a Y chromosome. The chromosome from the father determines the child’s gender. An X from the father would result in an XX combination, which is female. A Y from the father would result in an XY combination, resulting in a male child. So you want to find out about your genealogy by DNA testing?

Scientists don't understand how inheritance traits are selected. Two offspring’s from a set of parents may have different sets of chromosome pairs, and therefore different ancestral proportions even though they were the product of the same male-female union. This means if your mother was 50% Native American, you are not necessarily 25%. You may receive 10% Native genes and your sibling may receive 40%. For this reason, DNA testing for genealogy purposes may not give you the results you were expecting.

Your maternal copy of chromosome 1 could have been passed through your mother from your maternal grandmother OR your maternal grandfather, but which one you received was randomly determined at conception. The copy you receive from your mother is actually a chimeric chromosome that includes parts from your grandfather and your grandmother.

DNA Testing for Genealogy
Tracing your Family Tree through DNA testing has added a new dimension to genealogy. It can help verify if you are putting the right people in your family tree. If you have exhausted all sources and can’t go back any further, you can find out at least what your ethnic and genetic make up is.

Y-Chromosome testing looks at segments of DNA found only in males. The Y-STR genealogy DNA test is used to test males and their direct male relatives. The Y- Chromosome is passed from father to son relatively unchanged through many generations. Because the Y- Chromosome follows the same father-to-son pattern much like surnames in Western culture, the test has also been referred to as a "Surname Test."

MtDNA testing looks at the DNA inherited from your maternal ancestors. The two most common mtDNA tests are a sequence of HVR1 (Hypervariable Region 1) and a sequence of both HVR1 and HVR2.

Single nucleotide polymorphism (SNP) markers have an extremely low mutation rate. SNP markers, can indicate your haplogroup. There are at least two million SNPs in the human genome. Y-STR tests can predict your personal haplotype. Haplogroups are large groups of haplotypes. These results establish your deep ancestral origins dating back thousands of years, often geographically oriented. The haplogroups for males and females is different. Genealogy DNA tests show there is a rough overlap between Y-DNA and mtDNA haplogroups. If a female is tested and belongs to haplogroups A, B, C, D or X, and a male tested belongs to haplogroups Q or C3, they both would belong in whole or part, to a Native American group.

Autosomal STR markers, looks at the genetic material inherited from the mother and father in a lineal and non-lineal fashion. Each person inherits a unique combination of the autosomal STRs. It will help to identify the individual ethnic group and world regions where a person’s total combination of ancestry is most frequent or common. Some feel there are large margins of error with type of genealogy DNA test.

DNA Results
Most tests use STR markers known as short tandem repeats. The number of “repeats” of the same DNA sequence of A-C-T-G is known as “Alleles”. The markers are designated by a number. Example: one marker being tested could be DYS393 (DNA Y-Chromosome Segment) and results for the repetition of the sequence [AGAT] is 12. Thus the marker DYS393 has an allele of 12.

There are over 100 markers, but most genealogy DNA tests available are for 12 to 67 markers. The more markers you have tested, the greater the cost, but also narrows down your results with greater accuracy. If you test 12 markers, and you have another relative with the same surname, and same results (for the same STR markers and allele’s), your MCRA (most common recent ancestor) is between 7 and 29 generations ago. If you test 37 markers, your MCRA is between 2 and 7 generations ago. If you test 67 markers, your MCRA is between 2 and 6 generations ago. If you have a perfect match 12/12 with someone who does not have the same last name, your MCRA is probably about 1,000 years ago or 40 generations. If your last name is the same or a variant, then a match of 37/37 markers, gives you a 50% chance of having a MCRA within 5 generations.

The companies that are doing genealogy DNA testing do not use the same database or testing procedures. Therefore the same test, done at different companies, may result in different outcomes. This was uncovered when Oprah Winfrey and 60 Minutes did a segment revealing the same tests done from three (3) different companies, all had different results.

Comparing Genealogy DNA Testing Results
Y-Search is one company, pulling results from various genealogy DNA testing companies in an effort to help you find other people that have taken DNA tests from different companies to provide a link for possible genealogy matches. But remember, if your last name is not the same, your MCRA is about 1,000 years ago and will most likely not help you in your family research.

DNA Paternity Testing
Genealogy and DNA testing gives an ancient picture of your family and traces your roots back several thousands of years. A Y-STR comparison DNA test can achieve a probability of a relationship between a child, and his mother and father using a paternity Index (PI). The PI’s for each marker are multiplied with each other to produce a combined paternity index (CPI), which represents the overall odds, that an untested male would have the same results if his genetic profile were compared with the child’s. The CPI is then converted into a Probability of Paternity value, which specifies the probability that the tested man is the father.