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Value or Weight of Longest Segment vs Segment Shared in Determining Relationships

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  • Value or Weight of Longest Segment vs Segment Shared in Determining Relationships

    When you are looking at these two values in cM: Longest Segment and Shared Segments, which is more important?

    For example:
    1. Mother has a cM of 98 for the Longest Segment and 508 for Shared Segments
    2. Son has a cM of 97 for the Longest Segment and 297 for Shared Segments

    In looking at the research by Bettinger, he says:
    1. Half 1C average Shared vs Longest cM 458/75.
    2. 1C1R average Shared vs Longest cM 440/62
    3. Great Aunt Uncle average Shared vs Longest cM 844/86.
    4. Great Grandparent average Shared vs Longest cM 856/102

    If you were to give precedence to Longest Segment then Great Aunt/Uncle or Great Grandparent would be more appropriate, but if you give more weight to Share Segment value then Half 1C or 1C1R would be better.

    I have attached the chart I used
    Attached Files

  • #2
    Not a direct answer _ I suggest you read Blaine Bettinger's research work on shared cMs

    https://thegeneticgenealogist.com/20...ed-cm-project/

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    • #3
      These are just averages, but the ranges of possible shared DNA is wide. A real life example: one of my relatives shares 407cM with a 1C1R, longest segment 56 (according to FtDNA)

      In terms of steps of genetic distance a gt-grandparent and a gt-aunt or gt-uncle are the same. DNA alone can not tell you which it is, and it may even be some other relationship.

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