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Designating level of cousinship?

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  • prairielad
    replied
    Originally posted by josh w. View Post
    Thanks. Now it is less mysterious. Is there a source of this information.
    there are a few simple explanations in FAQ's
    https://www.familytreedna.com/learn/...tions-cousins/

    https://www.familytreedna.com/learn/...ionship-range/

    https://www.familytreedna.com/learn/...sidered-match/

    I don't think there is a in depth explanation of how FTDNA's algorithm works....

    Data in my previous post was just taken from a family members chromosome browser data for a suggested 3rd and 4th cousin.
    Last edited by prairielad; 17 May 2014, 08:39 PM.

    Leave a comment:


  • josh w.
    replied
    Originally posted by prairielad View Post
    I believe the total number of segments, their sizes(cM),and SNP Total all come into play.
    ie)3rd cousin
    CHROMOSOME CENTIMORGANS MATCHING SNPS
    2 1.38 500
    3 1.85 500
    3 2.81 700
    5 1.93 500
    6 1.5 4000
    6 1.57 500
    6 1.52 600
    7 2.04 500
    8 2.52 500
    8 2.2 500
    9 19.52 2795
    12 2.46 500
    17 2.61 500
    20 1.38 500
    45.29 13095SNPs

    4th cousin2 1.38 500
    3 2.61 600
    6 1.16 1200
    6 1.48 600
    7 2.48 500
    11 1.2 500
    12 2.46 500
    14 1.48 500
    15 2.56 700
    17 2.61 500
    18 21.92 2700
    19 2.3 600
    43.64 9400SNPs
    Thanks. Now it is less mysterious. Is there a source of this information.

    Leave a comment:


  • royfarnol
    replied
    @Josh W & Prairielad

    Thanks. I think you are both right.

    In my experience I get the impression that all my cousin forecasts are over-optimistic but since they seem arbitrary I suppose there are a lot of cases where the forecasts are under-optimistic?

    Leave a comment:


  • prairielad
    replied
    I believe the total number of segments, their sizes(cM),and SNP Total all come into play.
    ie)3rd cousin
    CHROMOSOME CENTIMORGANS MATCHING SNPS
    2 1.38 500
    3 1.85 500
    3 2.81 700
    5 1.93 500
    6 1.5 4000
    6 1.57 500
    6 1.52 600
    7 2.04 500
    8 2.52 500
    8 2.2 500
    9 19.52 2795
    12 2.46 500
    17 2.61 500
    20 1.38 500
    45.29 13095SNPs

    4th cousin2 1.38 500
    3 2.61 600
    6 1.16 1200
    6 1.48 600
    7 2.48 500
    11 1.2 500
    12 2.46 500
    14 1.48 500
    15 2.56 700
    17 2.61 500
    18 21.92 2700
    19 2.3 600
    43.64 9400SNPs

    Leave a comment:


  • josh w.
    replied
    Originally posted by josh w. View Post
    Because of adjustment for Ashkenazi endogamy, I have a fifth cousin with a shared cM of 150 and third cousins with shared cM of 80.
    and a third cousin with 50 shared cM.

    Leave a comment:


  • josh w.
    replied
    Originally posted by josh w. View Post
    Maybe they use a very arbitrary cutoff point for the combination of the two indices. All of your third cousins have a shared cM greater than 45.0 Only one fourth cousin does but with a lower longest block.
    Because of adjustment for Ashkenazi endogamy, I have a fifth cousin with a shared cM of 150 and third cousins with shared cM of 80.
    Last edited by josh w.; 17 May 2014, 10:06 AM.

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  • josh w.
    replied
    Originally posted by royfarnol View Post
    I don't see the logic in the numbers associated with these levels of cousinship. Is there something else taken into account that I don't know about? Thanks, Roy.

    Shared cM Longest Block
    4th Cousin 44.53 27.66
    4th Cousin 34.31 22.47
    3rd Cousin 50.16 21.89
    3rd Cousin 47.81 21.80
    4th Cousin 44.48 21.42
    4th Cousin 39.82 20.65
    4th Cousin 38.66 20.10
    4th Cousin 34.35 20.05
    4th Cousin 42.53 19.91
    4th Cousin 42.54 19.21
    3rd Cousin 46.43 18.56
    3rd Cousin 45.52 18.13
    4th Cousin 37.37 18.03
    4th Cousin 40.91 17.68
    3rd Cousin 50.96 17.38
    4th Cousin 65.83 16.59
    Maybe they use a very arbitrary cutoff point for the combination of the two indices. All of your third cousins have a shared cM greater than 45.0 Only one fourth cousin does but with a lower longest block.

    Leave a comment:


  • royfarnol
    started a topic Designating level of cousinship?

    Designating level of cousinship?

    I don't see the logic in the numbers associated with these levels of cousinship. Is there something else taken into account that I don't know about? Thanks, Roy.

    Shared cM Longest Block
    4th Cousin 44.53 27.66
    4th Cousin 34.31 22.47
    3rd Cousin 50.16 21.89
    3rd Cousin 47.81 21.80
    4th Cousin 44.48 21.42
    4th Cousin 39.82 20.65
    4th Cousin 38.66 20.10
    4th Cousin 34.35 20.05
    4th Cousin 42.53 19.91
    4th Cousin 42.54 19.21
    3rd Cousin 46.43 18.56
    3rd Cousin 45.52 18.13
    4th Cousin 37.37 18.03
    4th Cousin 40.91 17.68
    3rd Cousin 50.96 17.38
    4th Cousin 65.83 16.59
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