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Mini-Medical School #6 2018

Mini-Medical School #6 2018

Mini-Med #6- Genetic Genealogy #2

Stephanie Taylor MD PhD

Dec 1, 2018

“The problems before you are not as great as the ancestors behind you”


Although an apparently civilized society, we often know remarkably little about our family history. The availability of affordable genetic testing has opened a new area of personal discovery. This session will provide you with an overview of the developing field of genetic genealogy.

Before we look at benefits, let us explore the risks. Each of the big four testing companies have their own privacy policies. They will not share information with other companies, but you can upload your DNA data to third party sites such as DNAGedcom. Your genetic information is protected in part by the 2008 Genetic Non-discrimination Act of 2008. This Act prohibits employers (of companies of 15 or greater) from using genetic information in hiring, firing or promotion decisions and also it prevents health insurance companies from utilizing genetic information in their coverage decisions. This act does not limit life, disability and long term care insurance companies from making coverage decisions based on genetic information.

The Big Four: Ancestry, 23 and me, Family Tree and My Heritage DNA. The quality of the DNA sequencing is similar between companies, but it is the size and the relevance of the database that makes a difference in the interpretation of your results. The big four databases are primarily Northern European. Note that prices listed below change frequently.

23 and me Ancestry DNA Family Tree DNA My Heritage DNA
$69 $99 Varies with test $79.00
Ancestry and Health reports Largest database for building family tree at-DNA / mtDNA/Y-DNA Databases 100 million users; more international database, 1.7 million DNA profiles

Autosomal DNA testing

You have 23 paired chromosomes, and two of these are sex chromosomes, the X and the Y. Autosomal DNA testing generates data on those 22 non-sex chromosomes. All the testing services offer autosomal DNA testing, and this gives you the best profile for building family trees.

You inherit 50% of each parent’s DNA, and your children inherit 50% of your DNA. Each generation is halved due to the addition of the new genome from the partner. Even though the DNA is diluted through the generations, there are segments that are preserved and match up with related individuals. The degree of matching predicts genetic distance. Usually the closest match is parent/child, and the next closest is first cousin. Every testing company sets a minimum length of matching segments before calling it a match. Generally, they set the length to identify ancestors not more than 300-400 years in the past.

Each company has several web based tools to identify relatives, compare chromosomal segments, and for some, countries of origin.

Mt-DNA Testing

Mitochondrial DNA testing follows the maternal line. It is passed down from mother to both male and female children. Mitochondrial DNA is not part of the 23 Human chromosomes, but a part of the cell that generates energy. Unlike autosomal DNA, it changes slowly, and is very helpful in tracing distant ancestors and in getting past blocks in the family tree due to surname changes.

The small changes in the DNA are categorized into “haplogroups” which can represent family groups that go back thousands of years. The major European haplogroups are in the families of: H, J, K, T, V, X and U, as well as a few other candidate groups.

Y-DNA Testing

Y-DNA testing follows the paternal line. Each man passes his Y only to sons. Y-DNA, similar to mt-DNA, changes much more slowly than autosomal DNA and is useful for following the paternal line hundreds of years back in time. There are two methods of measuring Y-DNA. STR and SNP. STR means single tandem repeats and SNP means single nucleotide polymorphism (same as at-DNA). Each method identifies a haplogroup. There is active research in both Y-DNA and mt-DNA, and new data is added frequently. There is more information at: https://www.worldfamilies.net/yhaplogroups

Ethnicity Estimates

Most of the testing companies will give you estimates of your ethnic heritage. This will vary between companies based on the composition and size of their database, but most are roughly similar. As the database increases, the precision of the estimate increases dramatically.

Third Party Tools

You can load your raw DNA data into other websites for analysis. You should assess the privacy issues before uploading your DNA, but these sites can give you much interesting information, as the database is not limited to one commercial company. A complete list is on the International Society of Genetic Genealogy Site: https://isogg.org/wiki/Autosomal_DNA_tools


Family Tree Magazine https://www.familytreemagazine.com/

International Society of Genetic Genealogy https://isogg.org

Monterey County Genealogical Society https://mocogenso.org/