Back to Basics

DNA

Before I go much further I would like to take a little space here to talk about what Genetic Genealogy is and how it has taken Genealogy to a new level.

Genetic genealogy or genetic ancestry testing is the use of DNA to study ancient origins and relatedness between individuals.  When combined with traditional paper genealogy, it is a powerful tool for the genealogist’s toolbox.  There are four types of genetic ancestry testing: Y-chromosome (male), X-chromosome, mtDNA, and autosomal DNA test.

We all have 22 pairs of autosomal chromosomes of which each parent contributes half of each. This is the most commonly used testing used by genetic genealogy companies. It currently is the only one used by 23andme and Ancestry.com.   Autosomal DNA tests examine SNPs, or alleles to identify our ethnic origins. Autosomal DNA can also identify a majority of what “makes me me.”  Such as our hair and eye color, our preferences for sweet or salty foods, our height, the tendency to be overweight or underweight.  Mutations in these chromosomes can tell you what diseases you may be susceptible to, such as the brca1 breast cancer gene.  There is one thing it does not determine and that is your sex.  Only the male carries the Y chromosome, but he also carries the X or female chromosome.  Females carry two X chromosomes.

The Y chromosome is passed down from father to son without significant change. Over long periods of time the chromosome begins to accumulate mutations that are typically silent and have no impact on the carrier. These mutations, however, are useful for genealogical purposes – they can be used to analyze the relationships between populations and individuals.  FamilyTree DNA (FTDNA) offers three different Y DNA tests each measuring a different amount of genetic markers, varying in price related to the amount of markers tested.  There are other companies that offer this service but I am not familiar with them and don’t want to mis-state what is offered.

A male’s X chromosome is inherited from his mother and is a mixture of her two X chromosomes, one from her mother and one from her father. It is therefore a mixture of the maternal grandparent’s X chromosomes.

A female inherits one X chromosome from each of her two parents. The X chromosome from her father is passed on from his mother is a mixture of her parent’s (the paternal great-grandparent’s) DNA, while the X chromosome from the female’s mother is a mixture of her parent’s (the maternal grandparent’s) DNA.

Testing of the X chromosome is relatively new and FTDNA is a leader in this technology.  The problem with studying X is that the entire X chromosome undergoes recombination. In other words, in females the two X chromosomes randomly swap information and genes.

Mitochondrial DNA (mtDNA) is passed down almost unchanged from a mother to her children. That lets you trace your maternal ancestry using the world’s largest mtDNA database. FTDNA offers two levels of testing mtDNA. If you are an adoptee that is searching for your birth mother, this would be the way to go.  Or of course, it helps you to determine which side of the family a match is on.

All this being said about individual X and Y testing, if you do an autosomal test from anyone other than Ancestry.com they will identify your maternal and paternal haplogroup.  This will make it easier to identify which side of the family a certain match comes from, it is less specific, thus less trustworthy than the more detailed testing.  For instance, I have an H Mt haplogroup.  By comparing my H to other people with H they can make an assumption of where my mother and her mother etc. come from.  There are variations of the H such as H1, H1a and so on, which will change that assumption completely.  But if I am trying to identify if a cousin is from my maternal side or paternal side this is helpful.  Since I am not a male, I do not have a Y haplogroup.  If you can get a male family member to test, you could say that you are within that Y haplogroup, but it has to be someone with the same male paternal pattern, such as a male brother or son of your brother.

This is a very basic explanation of the different types of tests that are available.  Much of the information provide here is from the  ebook “I have the results of my genetic testing, now what?” by Blaine T. Bettinger, PHD J.D.  When combining genetic testing with paper (or electronic in most of our cases) you have a very dynamic tool.

 

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