Archive for DNA Basics

Second Cousins Surface!

I don’t want to get your hopes up, or mine, but the first 2nd and a related 2nd-3rd cousin have just surfaced on 23andMe.  Since their files appeared on 23andMe at the same time, they are highly likely to be sisters and likely once removed, that is, of the same generation as my sons.  They are much less likely to be 1st cousins to each other.  They are almost certainly not mother and daughter.

What does all that mean? They would be descendants of  Frank’s sibling(s).  Amazing.

We know that Frank went back into the US several times looking for a brother.  We don’t know when Frank or his brother were orphaned.  We don’t know if either of his parents survived, or had any other children.  We may be about to find out some of this.

On 23andMe, these two new cousins share the most genetic material with me outside of my brother Brian and sons Jon and David. The 2nd cousin shares with me, and some of you, 10 times more DNA than the next closest cousin found so far, a possible 3rd cousin.  The 2nd cousin shares 3.40% shared over 12 segments.  The 2nd-3rd cousin shares 2.4% over 9 segments.

It is possible that they link to me through my Scottish grandmother.  But since both these cousins have the K1a1b1a maternal haplogroup, which is seldom found in non-Jews and is found in only 10% of women in the UK, that possibility seems unlikely.  They are not linked through my mother who had the maternal haplogroup U4a1a.

I sent these cousins a note inviting them to share genomes.  However, these cousins may not agree to connect or share genomes.  23andMe has many members who do not want to make contact with others, for a variety of reasons.

This discovery is only two days old so contact with them, if it occurs, may be some time away.

Stay tuned.

Ian

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New Genetic Genealogical Resources – Kelly Wheaton’s Beginners’ Guide to Genetic Genealogy

I have begun reading this material and find it helpful. I hope that as I begin to use it that I will be even more helpful. At this site there are references to useful resources such as spreadsheets for consolidating data that can be sorted in many different ways.in order to find telltale patterns of chromosome segments that suggest branches on family trees..

http://www.yourgeneticgenealogist.com/2013/08/kelly-wheatons-beginners-guide-to.html?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+YourGeneticGenealogist+%28Your+Genetic+Genealogist%29

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DNA / Genealogical Comparison Guidance

Can you suggest texts that explain how to read chromosome segments so as to determine family tree branches?  A utility or  app into which to plug selected chromosome data and generate probabilities would be ideal. GEDmatch does not currently provide the triangulation utility which did help locate and populate potential branches which could then be matched against known family trees.

Thousands of cousins have  turned up via various genetic testing services.  The labs propose generational distance.

Certain individuals share the same chromosome fragment(s).   Clearly segments over 6 cMs strongly indicate cousinage probability and the larger the segments the stronger the probability.  One can then infer that, the more segments shared, the stronger the cousinage probability.  But how does one read those segments to get the most out of the analysis?

GEDmatch provides  several Admixture analysis utilities which shows you the regional DNA sharing for each segment of  each chromosome.  What is the value in this if one can then determine that shared segments contain specific regional contributions, e.g. north-east Europe, West Asia etc?

There are likely to be other bits of wisdom the appropriate books or utilities could provide.

Where are they?

Thanks.

Ian

 

 

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Graph showing genetic admixture for groups by % of genetic contribution by ancestors from specific regions

Source: http://2.bp.blogspot.com/_Ish7688voT0/TOAbjajWtcI/AAAAAAAAC40/GmUk005OYlU/s1600/ADMIXTURE10.jpeg

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Background on the process of diluted gene fragments passing from generation to generation

Here are some good resources to explain gene fragments passed down from a common ancestor to generation to generation.

http://www.isogg.org/wiki/Identical_By_Descent_segment

http://www.isogg.org/wiki/Wiki_Welcome_Page

http://www.isogg.org/wiki/Relative_Finder#Thresholds_for_relationship_matches

http://www.isogg.org/wiki/Autosomal_DNA_tools

There is an interesting user-controlled animation here:

http://learn.genetics.utah.edu/content/begin/tour/

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Sources: DNA Basics Explained

It is an oxymoron to state that DNA is complex. Fortunately, if you focus on the area that is important to you and if you use some of the many excellent resources that are available, you can understand what you need and apply it effectively.

Well that’s the theory. Stumbling is both frustrating and richly rewarding. After all, it is only about life and death, and so we might as well enjoy the ride.

As we come across resources that are reliable and have helped me, we will add them here.

It is also worth noting that we cannot assume that any “fact” or interpretation will be definitive for all time. DNA research is growing new knowledge at an exponential rate. The increasing number of people having their DNA analyzed is contributing to that.

It is also worth noting that what appears to be bona fide interpretation and analysis may not be reliable. Enthusiastic amateurs like me, without the rigour of peer review, can post anything and make it sound credible. Others post “analysis” which is really opinion or speculation. Still others, like me, conduct their research from a particular interest base which either corrupts their findings or states them in a way which is misleading because they do not take the time to qualify their findings or to put them in the appropriate context. Alas and, occasionally, mea culpa.

All of the retail DNA labs that I have checked out seem to have very good explanatory information. some of it is not so easy to find. There are other organizations, like the ones that I will list below, which provide great services as well, but many of them are hybrid blog/peer review so be careful about how you use information that you find there if it is critically important to you. Verify.

Retail Labs
23andMe (mine)
FTDNA

Information Sources
ISOGG International Society of Genetic Genealogy http://www.isogg.org/

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