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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

    The Shared cM Project is a collaborative data collection and analysis project created to understand the ranges of shared centiMorgans associated with various known relationships. As of August 2017, total shared cM data for more than 25,000 known relationships has been… Continue reading →


    • #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.


      • #4
        I need advice. My eight-year-old son is rapidly gaining weight. Our doctor says it’s genetics, but my husband and I have never been overweight. Could it be genetic?


        • #5
          Originally posted by capitulinagarage View Post
          I need advice.
          Get a second medical opinion!


          • #6
            By all means, get second opinion. Sudden weight gain in children is not normal. Suggest a physician specializing in internal medicine, if possible. "Genetics" is not likely to explain a sudden weight gain. Could be a metabolic abnormality or worse, but could equally well be something benign. Some basic tests could rule out some possibilities.