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Basic questions about chromosomes

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  • N43154
    replied
    A few comments on the discussion here. 1) The autosomal DNA segment analyzer and the alternative jWorks at dnagedcom.com are indispensible tools, far better than FTDNA's chromosome browser but not without problems. There is a learning curve to figure out your IBD clusters. 2) Forget the numbers. Except for close family members, atDNA doesn't really work by the numbers. It's handed down in a random and haphazard way. You can have an 8th cousin that matches you at 10 cm or a 3rd cousin. 3) Simply work the pedigrees in each IBD cluster until you get them back to the 1600s, if possible, and then look for overlapping ancestors. Don't stop with the first set you find.
    Last edited by N43154; 4 May 2015, 06:39 AM.

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  • IslaMel
    replied
    Chromosome Matching on GEDMATCH

    I have a question about matching more than one time on the same chromosome. What does it mean? On GEDMATCH I am finding people who appear to be related to me on several branches of my tree. Here is one example:

    Chr Start Location End Location Centimorgans (cM) SNPs
    3 3803076 4830348 3.0 381
    3 181318730 184563218 3.7 465
    6 17048497 18841195 3.0 417
    6 106704332 109568199 4.0 679
    7 717316 3017901 3.1 552
    7 72695953 76761486 3.5 473
    8 139325676 140625753 4.0 418
    10 70008984 71708405 3.4 604
    11 19008134 19977140 3.6 393
    12 108770029 113143382 3.9 868
    13 98871108 100544441 3.4 541
    13 108947427 109808079 3.6 357
    18 55781188 57652168 3.1 496
    19 55283511 56206434 4.7 301
    Largest segment = 4.7 cM
    Total of segments > 3 cM = 49.9 cM

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  • JaneDoe
    replied
    Originally posted by dna View Post
    What advantage does it offer above ICW feature of Family Finder?

    W. (Mr.)
    JWorks is explained here:

    http://dnagedcom.com/JWorks/Jworks_Kworks.pdf

    It seems to save hours of work is the main advantage.

    I've checked Matrix 1 on the FTDNA site. It is accurate including 'Duane' So 'Duane' is a valid overlapping segment.

    Why is Duane not showing any 'X's on FF??? As we each have two Chromosome's 1 and FF test both, is this the reason?

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  • dna
    replied
    Originally posted by JaneDoe View Post
    My first question is regarding Matrix 1. Am I right in assuming I share a common ancestor with all 11 people? Note there are no X’s for Duane.
    I am not familiar with JWorks.

    What advantage does it offer above ICW feature of Family Finder?

    W. (Mr.)

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  • JaneDoe
    replied
    My first question is regarding Matrix 1. Am I right in assuming I share a common ancestor with all 11 people? Note there are no X’s for Duane.

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  • JaneDoe
    replied
    This is a snap shot of the first two matrices.
    Attached Files

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  • JaneDoe
    replied
    Has anyone used the automated chromosome browser tool created by programmer Jay Pizarro called JWorks? It is a Microsoft excel macro that uses the FTDNA data to automatically create matrix building showing ICW matches. I've run my FTDNA data through this program. I need help to interpret what the matrices are telling me. In the next post I’ll show a snap shot of my first two matrices generated by this program for chromosome 1. The program generated about 60 of these matrices. I've colour coded these first two to help clarify and ask a couple of questions to anyone familiar with using matrices. Also I've changed the names in the interest of privacy.

    Thank you to anyone who will look at this and comment.

    I'll post my questions after I upload the chart and it's viewable.

    Leave a comment:


  • JaneDoe
    replied
    Originally posted by dna View Post
    That population is definitely undersampled.

    W. (Mr.)
    Yes and I'm starting to think this may be impossible to solve.

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  • dna
    replied
    Originally posted by JaneDoe View Post
    [----] I believe my grandmother’s ancestors may be from Russia.
    That population is definitely undersampled.

    W. (Mr.)

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  • JaneDoe
    replied
    These are the three ICW matches with my 1st cousin. (names edited for privacy)

    forum2.JPG
    Last edited by JaneDoe; 22 April 2015, 03:06 PM. Reason: added comment

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  • JaneDoe
    replied
    In mulling this over I can see my mistake. I share one unique grandparent with my 1st cousin. In other words we are half first cousins. If I have 5th cousins, only 1 in 10 will show up as matches and they will not necessarily be the same as my 1st cousins. So I cannot assume this 25% ratio for 5th cousins and above. The ratio would be closer to zero.

    As 4th cousins’ show up half of the time and 3rd cousins’ show up 90% of the time, do you think this statement is correct?

    As I share one unique grandparent with my 1st cousin, statistically I should expect just under 25% (say 20%) of my matches in the 2nd to 4th cousin range will be attributed to this grandparent’s ancestors.

    “Why the other match is obviously wrong?”

    That’s a great question and perhaps invalidates my above statement. There is a generation between my 1st cousin and our unique grandmother, namely our parents. it is possible matches are through the wrong parent. This is impression I have with the one match I believe may be invalid. I’m struggling with how these parents’ affect my above statement.

    I believe my grandmother’s ancestors may be from Russia.

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  • dna
    replied
    @JaneDoe

    One ICW match simply means that from the family branch that is common to both of you very few people tested. Very few in absolute numbers.

    You had proposed that your common family branch might be very small. It could be true, but in order to have many matches you need to have many people who had tested...

    W. (Mr.)

    P.S.
    Why the other match is obviously wrong ?

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  • prairielad
    replied
    Originally posted by JaneDoe View Post

    .............

    Do you have an opinion about why my results are so few?
    This could be due to a under test group within Database.

    For example my Paternal Grandmother was born in Romania.
    With a distant cousin who is in the 2nd to 4th Range who shares a same ancestral surname from the same location and timeframe, they only share 2 ICW matches.

    My Grandmothers kit only has 105 matches not including immediate family

    where as my fathers paternal side with Irish/Scottish ancestry seems to be one of the more tested groups

    Edit
    of the 105, 100 of those matches are in the Speculative Category (4th to Remote)
    Last edited by prairielad; 22 April 2015, 02:12 AM. Reason: added

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  • prairielad
    replied
    above mentioned numbers do not include ourselves as matches to one another. Included each kit has an additional 10 matches on each of our match lists and ICW lists

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  • JaneDoe
    replied
    Oh, Thank you for the detailed list. I'm mainly interested in the number of ICW matches you have, with your 1st cousin 1X. If you take all of the close relationships out of the equation would that number for you be about 60 in your case? That would make sense.

    In my case it seems my grandmother's ancestors perhaps didn't have many offspring. I loaded my results into GEDMATCH for a similar comparison, and it only returned one match. I was using the default settings.

    Do you have an opinion about why my results are so few?

    Leave a comment:

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