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  • differences in DNA for same relationship

    Can anyone explain the difference to me as this is the same relationship?
    My mother and my cousin (her maternal aunt):
    Suggested relationship---------1st cousin
    relationship range---------------1st cousin, aunt, uncle, niece
    shared cm------------------------747.76
    longest block--------------------90.88

    My husband and paternal aunt and maternal uncle:
    Suggested relationship-------half sibling, grandparent/grchild
    Relationship range------------half sibling, grparent/child, aunt,uncle,nephew
    shared cm----------------------1928.62 aunt
    shared cm----------------------1910.91 uncle
    longest block------------------112.62 aunt
    longest block------------------142.38 uncle

    There is a large difference in the amount of DNA shared by my husband and his aunt and uncle and my cousin and her aunt. Can anyone explain this to me?

    This is how I match my cousin:
    suggested relationship------- 2nd cousin
    relationship range--------------1st to 3rd cousin
    shared cm-----------------------283.97
    largest block -------------------35.42
    Last edited by LSSmith; 5 April 2011, 09:05 AM.

  • #2
    I'm sure others will have more detailed scientific explanations regarding whether the difference is due to the normal range of outcomes.

    One possibility I would consider is that your husband's parents may share some distant ancestors. This is because both his paternal aunt and maternal uncle have similar total shared cM. GEDMatch has a utility that will look at the raw data from one kit (your husband's) and see if his parents are "related".

    Comment


    • #3
      Originally posted by GayeSherman View Post
      I'm sure others will have more detailed scientific explanations regarding whether the difference is due to the normal range of outcomes.

      One possibility I would consider is that your husband's parents may share some distant ancestors. This is because both his paternal aunt and maternal uncle have similar total shared cM. GEDMatch has a utility that will look at the raw data from one kit (your husband's) and see if his parents are "related".
      Gaye
      Thanks so much for the response and idea however, I went to gedmatch and they don't match one little bit. Any other ideas or explanations?

      Comment


      • #4
        Yes this is normal. Recombination is very unpredictable. Every child will have different combinations from its grandparents, great grandparents, etc.; no two are the same.

        Comment


        • #5
          Originally posted by mkdexter View Post
          Yes this is normal. Recombination is very unpredictable. Every child will have different combinations from its grandparents, great grandparents, etc.; no two are the same.
          I am confused. I know that each child gets 50% of their DNA from each parent. I assumed that for each subsequent generation the number would divide etc. At this time my husband has more than double the number of matching DNA with his aunt and uncle than my cousin and my mother. I understand how DNA recombines however, what I don't understand is how the numbers vary. I must be confusing terminology as I am honestly perplexed. Can someone give the DNA for dummies explanation?

          Thanks
          Linda

          Comment


          • #6
            Originally posted by LSSmith View Post
            I am confused. I know that each child gets 50% of their DNA from each parent. I assumed that for each subsequent generation the number would divide etc. At this time my husband has more than double the number of matching DNA with his aunt and uncle than my cousin and my mother. I understand how DNA recombines however, what I don't understand is how the numbers vary. I must be confusing terminology as I am honestly perplexed. Can someone give the DNA for dummies explanation?

            Thanks
            Linda
            each child gets 50% of their parent but each child will get different DNA passed down from their parents unless identical twins. Siblings will have some DNA same and some different. This is why they tell you the more people you test in your family the better at finding connections since each one of you will have different DNA inheritance.

            Comment


            • #7
              Originally posted by LSSmith View Post
              I am confused. I know that each child gets 50% of their DNA from each parent. I assumed that for each subsequent generation the number would divide etc. At this time my husband has more than double the number of matching DNA with his aunt and uncle than my cousin and my mother. I understand how DNA recombines however, what I don't understand is how the numbers vary. I must be confusing terminology as I am honestly perplexed. Can someone give the DNA for dummies explanation?

              Thanks
              Linda
              We have 23 pairs of chromosomes. One set is paternal and the other maternal. That is where the 50% comes from. It has nothing to do with the mixture the grandkids receive.

              If you take those paternal and maternal chromosomes and recombine them into a unique assortment, 43%-57% or 55%-45% or 50%-50% combinations of paternal and maternal you have the mixtures. This happens in the non-paired (haploid) chromosome gametes. The non-paired chromosomes then combine with the other parent's non-paired haploid cell and you once again have the paired (diploid) 23 chromosomes in the child. The child has a mixture of paternal as well as maternal grandma and grandpa's DNA recombined in each of its 23 chromosome pair.

              Example:

              my son has 100% match to my DNA. That's his paternal DNA in FF
              my son has 100% match to his mother's DNA. That's his maternal DNA in FF

              my granddaughter has her own set of paternal and maternal DNA. Looking at her paternal chromosomes she has 100% match to her father.

              Here's where the mixture comes in. We look at her and compare to myself, my wife, my mother, my father.

              my granddaughter has 67% of my DNA in her paternal chromosome set
              my granddaughter has 33% of my wife's DNA in her paternal chromosome set.

              we keep going...

              my granddaughter has 53% of her great grandmother's DNA in her paternal chromosome set (this is out of the 67% from me and it is contributed by my mother via me via my son to her)
              my granddaughter has 47% of her great grandfather's DNA in her paternal chromosome set (this is contributed by my father via me via my son to her).

              this chart is my granddaughter's test compared to me and my wife. It's her paternal DNA in FF.



              Hope that helps.

              MD.
              Attached Files
              Last edited by mkdexter; 6 April 2011, 12:01 PM.

              Comment


              • #8
                Now I'm even more confused

                Originally posted by mkdexter View Post
                We have 23 pairs of chromosomes. One set is paternal and the other maternal. That is where the 50% comes from. It has nothing to do with the mixture the grandkids receive.

                If you take those paternal and maternal chromosomes and recombine them into a unique assortment, 43%-57% or 55%-45% or 50%-50% combinations of paternal and maternal you have the mixtures. This happens in the non-paired (haploid) chromosome gametes. The non-paired chromosomes then combine with the other parent's non-paired haploid cell and you once again have the paired (diploid) 23 chromosomes in the child. The child has a mixture of paternal as well as maternal grandma and grandpa's DNA recombined in each of its 23 chromosome pair.

                Example:

                my son has 100% match to my DNA. That's his paternal DNA in FF
                my son has 100% match to his mother's DNA. That's his maternal DNA in FF

                my granddaughter has her own set of paternal and maternal DNA. Looking at her paternal chromosomes she has 100% match to her father.

                Here's where the mixture comes in. We look at her and compare to myself, my wife, my mother, my father.

                my granddaughter has 67% of my DNA in her paternal chromosome set
                my granddaughter has 33% of my wife's DNA in her paternal chromosome set.

                we keep going...

                my granddaughter has 53% of her great grandmother's DNA in her paternal chromosome set (this is out of the 67% from me and it is contributed by my mother via me via my son to her)
                my granddaughter has 47% of her great grandfather's DNA in her paternal chromosome set (this is contributed by my father via me via my son to her).

                Hope that helps.

                MD.
                Matt,

                Thank you for your patient explanation. But now I'm even more confused.

                Are you saying that I don't have 50% of my father's DNA and 50% of my mothers? That, instead, I could have 60% of my father's and 40% of my mothers?

                Vivian

                Comment


                • #9
                  Originally posted by mkdexter View Post
                  We have 23 pairs of chromosomes. One set is paternal and the other maternal. That is where the 50% comes from. It has nothing to do with the mixture the grandkids receive.

                  my granddaughter has 53% of her great grandmother's DNA in her paternal chromosome set (this is out of the 67% from me and it is contributed by my mother via me via my son to her)
                  my granddaughter has 47% of her great grandfather's DNA in her paternal chromosome set (this is contributed by my father via me via my son to her).

                  Hope that helps.

                  MD.
                  Yes it does very much and thank you but.....
                  When we look at matches in FF it tells how many shared CM one has with the person. This is what my question is about the amount of shared cM. Maybe I don't really know what shared CM means. How much CM does one person have? Would you have equal amounts of matching CM to each parent?
                  I am reposting this from my first post. See how much more CM in my husbands matches? Is CM coming from both sides of the family? That is what is confusing me. When I first looked at my cousins amount of CM I thought that it might be possible that my mother (cousins aunt) and her brother (cousins father) do not have the same father, although I don't really think that to be true. My husband is showing a total of 3838 CM between his uncle and aunt. My cousin shows 747 in a match with my mother. Does that mean that 3091 CM matches her mothers side of the family? Am I making myself clearer?

                  My mother and my cousin (her maternal aunt):
                  shared cm------------------------747.76
                  longest block--------------------90.88

                  My husband and paternal aunt and maternal uncle:
                  shared cm----------------------1928.62 aunt
                  shared cm----------------------1910.91 uncle
                  longest block------------------112.62 aunt
                  longest block------------------142.38 uncle
                  Last edited by LSSmith; 6 April 2011, 12:16 PM.

                  Comment


                  • #10
                    Originally posted by LSSmith View Post
                    I am confused. I know that each child gets 50% of their DNA from each parent. I assumed that for each subsequent generation the number would divide etc. At this time my husband has more than double the number of matching DNA with his aunt and uncle than my cousin and my mother. I understand how DNA recombines however, what I don't understand is how the numbers vary. I must be confusing terminology as I am honestly perplexed. Can someone give the DNA for dummies explanation?

                    Thanks
                    Linda
                    The 50% number is exact for parent / child (disregarding X, Y, and mtDNA), because you inherit one copy each paired chromosome from them. However, each time the parent creates a sperm or egg for the next generation, it is a random selection of DNA segments from his/her parents. Just as you don't always get 5 heads and 5 tails if you toss a coin 10 times, the amount inherited from each of the child's grandparents can be more or less than 25%.

                    This web page gives some idea of the ranges observed with known relationships. The stats are for 23andMe, which only counts segments over 5 cM in size, so the absolute numbers will be different for FTDNA. However, it does show the big ranges encountered.

                    http://isogg.org/wiki/Autosomal_DNA_statistics

                    Another way to explore this is to look at the Mendel family at 23andMe. You can create a demo account to see this. It shows three generations, and you can see how each of the grandchildren inherited different sections and amounts from the grandchildren.

                    Comment


                    • #11
                      Originally posted by vivianruth View Post
                      Matt,

                      Thank you for your patient explanation. But now I'm even more confused.

                      Are you saying that I don't have 50% of my father's DNA and 50% of my mothers? That, instead, I could have 60% of my father's and 40% of my mothers?

                      Vivian
                      No. Vivian that was one example. You have a paternal set and a maternal set of chromosomes that make up a pair of 23 chromosomes. That is 50% and 50%. But inside of those 1/2 and 1/2 you will have mixtures from your grandparents.

                      Comment


                      • #12
                        Originally posted by LSSmith View Post
                        Yes it does very much and thank you but.....
                        When we look at matches in FF it tells how many shared CM one has with the person. This is what my question is about the amount of shared cM. Maybe I don't really know what shared CM means. How much CM does one person have? Would you have equal amounts of matching CM to each parent?
                        Yes you have an equal amount from each parent. The total is about 3380 or close to it in cM right now. This number will change up or down as they tweak the tests, remove the SNPs they report, etc. A parent and child will have 3380cM shared DNA. The other parent will ALSO have 3380cM shared DNA to the same child.

                        The confusion arises because people try to make a pair a quantity. That's not it. You have to split the pair and and then you can see it like FF sees it. You get 1/2 a pair from each parent but you read 1/2 the pair as a full paternal or a full maternal match. You have paternal and maternal ancestors so therefore when you compare segments in FF or RF you are seeing 1/2 a pair compared to 1/2 a pair.
                        Last edited by mkdexter; 6 April 2011, 01:09 PM.

                        Comment


                        • #13
                          What probably confuses people is that FF and RF report differently.

                          RF reports a % and FF reports a shared cM and longest block.

                          Don't look at the two tests the same way.

                          FF uses lineages only. It shows you a reading based on one lineage, not the pair, not both lineages.

                          MD.

                          Comment


                          • #14
                            Here's three real-life examples from my relatives, using stats from here <http://www.isogg.org/wiki/Identical_By_Descent_segment>:

                            first cousins who share 746 cM (expected range: 548-1034 cM)
                            second cousins who share 238 cm (expected range: 101-378 cM)
                            fourth cousins who share 11.5 cM (expected range: 0-50 cM)

                            In these examples, the first cousins have less than average for their relationship but are still within range, while the second cousins have bang-on the expected amount.

                            The fourth cousins also have less than average, but are still within range, and note that it's possible to have no matching at all with fourth cousins (this will happen something like 10% of the time).

                            Does that help?

                            Comment


                            • #15
                              Originally posted by LSSmith View Post
                              My mother and my cousin (her maternal aunt):
                              shared cm------------------------747.76
                              longest block--------------------90.88
                              I am a little confused too.. How can your mother's aunt be your cousin? She would be your great aunt.

                              Comment

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