Monday, February 5, 2018

Program Review - Marti Lewis on "Exploring Your DNA Results"

There were 34 in attendance for the CVGS program meeting on 31 January at the Chula Vista Civic Center Branch Library.  

The speaker was Marti Lewis who discussed "Exploring Your DNA Test Results."

Marti said there were many ways to use DNA to trace your Family History.  The main question most people have is "what do we do with it?"  

Each person receives 23 pair of chromosomes from their biological parents - 22 pair are autosomal chromosomes, and 1 pair of sex chromosomes: Males receive a Y-chromosome from their father and an X chromosome from their mother;  Females receive an X-chromosome from each parent.

There are three types of DNA testing that deal with your 23 pairs of chromosomes:

*  Y chromosome:  A sex chromosome transmitted from fathers to sons.  This follows the paternal line (e.g., 1 of your 32 3rd great-grandparents).

*  Mitochondrial DNA:  Matter outside the cell nucleus, transmitted from females to children.  This follows a maternal line (but males don't pass it on) (e.g., 1 of your 32 3rd great-grandparents).

*  Autosomal DNA:  The DNA on 22 chromosomes that are passed from all of your ancestors through your parents (e.g., all 32 of your 32 3rd great-grandparents).

With Y chromosome and mitochondrial DNA tests, you can determine the haplogroup of the paternal and maternal lines - where did they originate, where did they migrate to in ancient times.  The Y-DNA haplogroups differ from the mtDNA haplogroups.  For instance, Marti's mtDNA  haplogroup is L3e, which came from Mozambique.

AncestryDNA, 23andMe, FamilyTreeDNA and MyHeritageDNA offer autosomal testing, but only FamilyTreeDNA provides Y-chromosome and mitochondrial DNA tests.  23andMe does provide haplogroup definition as part of their service.

What can you learn from your Autosomal DNA test?

*  Ancestry Composition - your ethnicity, according to how your DNA matches the test company's reference groups.  Marti's ethnicity estimate shows that she is 65% Sub-Saharan African, 32.2% European and 1.8% East Asian/Native American.

*  Compare your DNA to your matches - the percentage of DNA you share helps determine the possible relationships to your matches.  Each DNA match on your list will tell you how much you share with that person.  Typically, you share 50% with a parent, 25% with a grandparent, 12.5% with a great-grandparent, etc.  A first cousin will share about 12.5% with you, a 2nd cousin about 3%, a 3rd cousin about 0.8%.

*  Find common ancestors with your DNA matches.  She explained the concept of cousins and removed cousins - a 3rd cousin shares 2nd great-grandparents, and a 3rd cousin once removed would share common ancestors 4 generations back for one person, and 5 generations back on the other line, in other words one generation different from a common ancestor.

Marti described one of her autosomal DNA matches - William Paxson Gordon (a white man), with whom she shares 26 cM in 2 segments, meaning he is probably a 3rd cousin 1x removed, with common second great-grandparents.  One of Marti's second great-grandmothers is Cynthia Jane Paxson (1825-1886) whose father had one of William Gordon's Paxson ancestors.  

She said that it helps to have an online Family Tree that your family and cousins can find and use - Marti's is on the Tribal Pages website.   The site is free, although there is an annual fee for image storage.

Marti has found that DNA testing and analysis has helped unravel some of her family history mysteries.  In some cases, DNA test analysis can strengthen your research paper trail, and help you avoid false connections.

This was a good introduction to DNA testing and analysis for CVGS members.

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