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I received my 23 and me results and it says I share 52% DNA with my mom.

Is this possible?

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This could also be explained if the parents share DNA. If you took the same test with your father and it also was > 50%, it could indicate they are distantly related. A single shared chromosome could appear as ~52%. Even if dad only shows 50%, he could have passed the shared DNA but mom did not pass it down, so it would overlap with the DNA mom did not pass down.

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    It is a possibility. My dad passed away years ago though. Looking at my ancestral tree I also noticed that some distant cousins are on both my mom and dad’s side. Weird question coming up. Can siblings share 52% DNA? My mother had an abusive father. So I guess what I am asking is could May mother also be my sister?
    – Anónimo
    Feb 22 at 14:22
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    @Anónimo: That would result in a much higher percentage of shared DNA, on the order of 75% or so. 52% is close enough to one half that any shared ancestry between your parents must be several generations back. (Mathematically, your parents having a shared great-great-grandparent would make the expected coefficient of relationship between you and your mother about 53.1%, while going back one more generation would make it 51.6%. But the actual amount of shared DNA can be different, since inheritance is to some extent a random process.) Feb 22 at 14:53
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    Siblings can share anywhere from 0% to 100%, but generally it averages around 50%. If you are asking if your grandfather could be your father based on that small overlap, that is extremely unlikely, not impossible, but very unlikely. Since you have already identified an overlap in the family tree, this would most likely explain it.
    – rtaft
    Feb 22 at 15:00
  • Thank you all for your kindness and time in explaining this to me.
    – Anónimo
    Feb 22 at 15:39
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The sex chromosomes are likely what make up the discrepancy. I'm guessing you are male.

Females will share exactly 50% of their DNA with each parent, since they inherit 22 autosomes from each parent, and an X-chromosome from each parent.

Males will share slightly more DNA with their mother than their father, since they also inherit 22 autosomes from each parent, but inherit an X-chromosome from their mother, and a Y-chromosome from their father. The X-chromosome contains significantly more DNA than the Y-chromosome. Therefore, as a percentage of DNA inherited, sons get a little more from their mother.

23andMe note in their Average Percent DNA Shared Between Relatives that parent-child relationships will share "50% (but 47.5% for father-son relationships)". Or if you calculate it the other way, 52.5% for mother-son relationships. The sex chromosomes presumably account for this difference. Many "autosomal" tests such as 23andMe also include many markers on the X-chromosome, and sometimes some on the Y-chromosome.

Of course, when DNA testing is performed there may also be some small margin of error, so these numbers may not match absolutely perfectly in each case, but they should always be close.

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    Interesting. I read that too but I am in fact female, with two children and no chromosomal abnormalities.
    – Anónimo
    Feb 22 at 9:58
  • @Anónimo very interesting, that surprises me. I don't have a good explanation other than error, or possibly your parents being related. On 23andme can you see in the chromosome browser where the "extra" DNA is coming from?
    – Harry V.
    Feb 22 at 15:33
  • You could also upload to Gedmatch and in One-to-One compare look to see if there are any long lengths of full match (should be mostly half match).
    – Harry V.
    Feb 22 at 15:39
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    "23andMe analyzes your DNA by looking at certain genetic variants across the entire genome" - would the results change if they actually compared entire genomes?
    – Mazura
    Feb 22 at 17:30
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    @Mazura If they compared entire genomes I would expect well over 90% similarity between any two people. The point is to find genes that may actually change between individuals. And even unrelated (or very, very, very distantly related) people share genes (take two white-skinned, blonde-haired, blue-eyed people, they will share genes even if they are not related). Filiation guarantees that at least 47.5-52.5% are common (based on sex of the two people), but it's not unexpected that you may share more (it means your parents share some genes). The exact figure will depend on what genes are tested
    – jcaron
    Feb 23 at 11:18

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