April 27, 2015

How Much DNA Do You Share With Your Blood Relatives?

How much genetic material do you share with your biological relatives?  Take a look at the family tree below and the figure in the red box is the percentage of genes your body has in common with your blood relatives.  For example, your first cousin has 12.5% of the genes you do (implying, inversely, that 87.5% of their genes are different).  Your third cousin twice removed, on the other hand, would have only 0.195% of the same genes, meaning 99.805% of their genes would be different.  This assumes, of course, that you have no double relations in your family tree (e.g., sharing a great-great grandmother from two sides of your family tree).  

DNA Shared Between RelativesThe chart also ignores relatively rare phenomenon such as the elusive double cousin.  These relationships arise when two siblings of one family reproduce with two siblings of another family.  This results in the children being related to each other through both parents, and sharing the same grandparents.  As a result, double cousins are genetically equal to half-siblings, sharing double the genetic material normally seen in first cousins.  

  • Doug

    Not sure I understand. I would expect to share well over 99% of DNA with my immediate relatives. How do you calculate that I share only 50% DNA with them?

    • Joshua Kennon

      Your body was created by taking roughly 50% of the genes from your father and 50% of your genes from your mother.  If you have siblings, different genes in different combinations were passed onto then due to sexual reproduction creating a roulette effect, resulting in siblings sharing roughly 50% of the genetic material, as well.  

      The exception is identical twins, who share 100% of DNA due to coming from the same egg and the same sperm, which split and began reproducing independently from the same gene pool combination.

      On a related note, a common misconception is that identical DNA must result in identical outcomes.  Identical twins, for example, have different fingerprints, which you can read about here: http://www.nytimes.com/2009/10/06/science/06qna.html.  If one twin suffers from autism, there is only a 90% chance the other will, too (not 100%).  If one twin is gay or lesbian, there is only a 50% chance the other is too (not 100%), etc. etc.  This is because of, in simplified terms, the fact that our genes have ‘on/off’ switches attached to them that can be flipped through conditions in the womb, environment throughout life, exposure to certain chemicals, and a host of other factors.  For a very basic explanation of how genes get flipped on or off, read http://www.thetech.org/genetics/ask.php?id=63

      And, of course, it’s fascinating how our ancestral DNA plays a role in our day-to-day lives.  Most of the humans alive on planet Earth cannot drink milk; the figure is around 70% for adults.  If you live in the United States and are white, though, you wouldn’t realize this because your ancestors developed a mutation that allows us to process cow’s milk.  This explains more: http://www.thetech.org/genetics/ask.php?id=250

      If you prefer a hierarchy written out, Genealogy.com has that at http://freepages.genealogy.rootsweb.ancestry.com/~laetoli/degree.html

      • Doug

        Ahh ok.. it is just a semantic difference then. I was comparing your percentage to statements like “Humans share 98% of their DNA with chimps”. That percentage is about how much of the data contained in the DNA is the same regardless of ancestry, where you are talking more about the bloodline path of where it came from.  Thanks for the clarification!

        • http://andrewdouglass.com/ Andrew Wells Douglass

          I agree the “DNA shared” figures are misleading. They make it sound as if there were an infinite numbers of genes, when of course there are only so many ways to code for whatever protein. Perhaps it would be better stated as “probability you share a given gene because of shard ancestry” for, say, eye color (which is itself polygenic, not blue-or-brown as taught in grade school!). Some genes also tend to be transmitted together. You share some/many genes by pure coincidence. Thanks.

      • TL Howard

        Actually, the most recent and large sampled research (Australian Twin Registry) plus another (forgot its name, sorry) shows that the concordance of monozygotic for homosexuality (male) is only 20%. There is obviously a biological cause/trigger (with only a genetic susceptibility to that environmental trigger) to male homosex.

      • Drakkar77

        The gene that processes lactose can be switched back on by consuming enough milk, at least in some people. Epigenetics is still a rather new science and so it’s not understood as well yet.

      • Matthew

        Am I 50% my father and 50% my mother then? Am I not unique? Is there anything unique about me? I dont want to be 50% someone and 50% of someone else :(

        • http://www.joshuakennon.com/ Joshua Kennon

          Your genetic material is but the combination results in a completely new, never-before created outcome that is entirely unique.

        • Matthew

          But still that combination is 50% my mother and 50% my father??? It makes me feel sick.

        • -A

          I actually think it’s a beautiful thing. You come from both your parents, but are made from a very unique combination of their DNA – as well as that of your grandparents, great grandparents, etc.

        • Matt

          Are you serious? How does that make you feel sick?? That’s the entire point of replication.. survival. We are the result of everyone who has come before us. (see what I did there?)

        • Matthew

          It makes me feel sick because it means there is no me. If im half my mother and half my father, wheres the me part? See what I didnt do there…?

        • Frank

          No I don’t. By your definition no organism that has ever lived is much of themselves. Only thing that are more “themselves” than the rest are tumours. Trying to relate the “you” as a philosophical term to genetics is just plain dumb.

        • Matthew

          Tw*t. Off course you didnt see what I DIDNT do there.
          Im glad my question revealed your non-existent sense of self, and you then reintergrated yourself by making the source (my question) invalid. Too “philosophical”?

        • Jeff

          It makes me feel sick how dumb you really are, Matthew.

        • Matthew

          There we are then thanks very much.

        • Matthew

          Did you read Franks comment before you responded? And dont use my name like you know me, Jeff/tw*t.

        • jamiinvegas

          Actually you are more closely related to your mother genetically than your father.

        • BarbB

          It sounds to me as if your parents are not very nice people and you don’t want to be like them. Your genetic makeup is not your destiny. Your height is a trait that is highly determined by your genes, but whether or not you are kind is something over which you have a high degree of control.

      • Zachary Johnson

        It’s basically 0.5 to the power of X where X = the amount of tiles you move across from child to parent to find the relevant relative.

    • William_JD

      How does he calculate that? By using sloppy thinking.

  • K

    What are the figures for half-sibling relationships?

    • http://www.joshuakennon.com/ Joshua Kennon

      Cut the sibling percentages in half.

      • Beetlejuice118


  • Tashina

    I found out I have a cousin whos dad is my mom’s scound cousin. And his mom is my dad’s scound cousins aswell, how much DNA do we share?

    • marinegolfer68

      depends on what time the train left New York… actually according to the chart, the become closer related dna wise… this cousin would be the same as a first cousin (per dna) to both your mom and dad which would make a second cousin for you (per dna) 6.25

  • http://www.joshuakennon.com/ Joshua Kennon

    This is a joke, right? Please tell me you realize the numbers shouldn’t add up to 100% …

    • Zachary Johnson

      Yh, its supposed to be 50% to the power of P where P = the amount of relatives you go through and including yourself as +1. So 0.5^P+1 Mathematically its impossible

  • http://www.joshuakennon.com/ Joshua Kennon

    Again, this is a joke, right? …

    • Frank

      There are people believing Santa Claus is invented by Coca Cola and the moon is made of cheese, what can you do.

  • John Tate

    Why would the numbers add up to 100

  • jjay09

    why is it that even charts displaying the family tree is done so in a such a sexist way

    • http://www.joshuakennon.com/ Joshua Kennon

      Given that there were two possible ways this chart could have been presented by whomever designed it, it is impossible to say whether or not the chart is presented in a sexist way as there was a 50% probability of either the paternal or maternal lineage being used as the illustration (a complete family tree would have been more difficult to read and therefore not as optimal to utilize as a visual aid so we will exclude it from the analysis).

      Absent other information, a determination of sexism is impossible. For example, had a maternal family tree been used, a man could have claimed it was sexist but it would not make it so. There simply isn’t enough evidence to indicate either way.

      Without said evidence, or any additional supporting data, the conclusion that the chart is sexist is a form of subconscious confirmation bias meant to strengthen a present conviction in the observer that reinforces preconceived ideas.

      (An an interesting discussion of second and third order effects, one could argue, upon studying, say, 100 textbooks with family trees in them, that a distribution that represented more than an approximate 50/50 split would be sexist but even this would be problematic as people are influenced by their life circumstances. In the lower and middle classes, nearly 1 out of 2 boys are now born to a mother out of wedlock, which would theoretically lead to a higher probability of them using her bloodline if they were preparing a chart such as this, skewing the results in favor of women. On the other hand, given past legal precedence based on the nearly now-defunct patriarchal structure of marriage a century ago, names are passed down from the male in almost all cases as a result of cultural practice, meaning that a person might be more interested in knowing where his or her namesake originated due to a myriad of subconscious forces, such as mere association tendency (which is so powerful, there is overwhelming statistical evidence that boys with names like “Dennis” become dentists far more likely than should be the case; it’s the way the human mind pulls us in certain directions). Therefore, you could expect the distribution to favor males. Still yet, whomever prepared the chart could be a medical student studying Y-STR on the Y-Chromosome and want to illustrate the unique situation found exclusively in males that causes each and every person on the male only chart to share an identical copy of nearly half the genetic material that composes their body.)

      TL;DR: It is mathematically impossible based on present evidence to conclude whether there was any form of gender preference in the creation of the chart.

      • Jonelle

        try this article – Charlemagne’s DNA and Our Universal Royalty

        We’re all probably related!

      • Re

        The only thing that needs to be done to satisfy this person would be to
        list the women first and then show the men as subservients to the women,
        and then maybe to add a 50 in the mother box and a 25 in the
        grandmother box and so on. This chart has been simplified to remove any
        redundancies because everyone is assumed to know that the mother and the
        father are on the same level and there is no such subservience unless
        you are reading into the chart that way, and then if you were, then she too is sexist in your own way (reverse discrimination). (I hope I am not being sexist by assuming that JJay is female.)

  • stacie

    I have a first cousin that i believe is my half brother what would the percentage be if we did a dna test?

    • http://www.joshuakennon.com/ Joshua Kennon

      If he is your cousin, 12.5%. If he is your half brother, 25%.

      • regina

        I had my father’s nephew take the test, his test came back 20 something % and my father’s niece also took test and she shows about 12% so what am I looking at a possible 1/2 sibling. The nephew is my fathers brothers child and the neice is my fathers sisters child. so they would be my first cousins,right, with the chance the nephew is actually my 1/2 sib.

        • Beetlejuice118

          The tests said you share roughly 20% with your male cousin and only 12% with your female cousin? If that’s the case your dad fucked his brother’s wife and she had his baby. I’m assuming you’re trolling though because your family would have split up the minute the test came back and punches would have been thrown

        • regina

          Actually they are all gone, so there is no way of knowing for sure, other than the facts of the DNA profiles. Thanks for the response. I will be taken my theory to the grave with me.

  • Jay Sullivan

    This chart is completely wrong. This is not taking into account that the most unrelated people in the world share about 99.5% of their DNA. Taking that into account, siblings share about 99.75% of their DNA ((100% + 99.5%) / 2). Cousins share about 99.615% ((99.75% + 99.5%) / 2). Second cousins share about 99.5575 ((99.6125%+99.5%) / 2), third cousins 99.52875, etc.

  • Melissa Ramirez

    What is he if we have the same Grandmother but different grandfathers? Do we have the same blood?

    • http://www.joshuakennon.com/ Joshua Kennon

      You would cut the appropriate figures in the chart in half (divide by 2) as you share half the common ancestors.

  • wayne

    I assume when you say siblings share 50% genes that this is for all practical purposes an approximate figure. If I have 4 brothers, they all share 50%, yet a different combination of the original pool?

  • Rae

    Not sure I am understanding. I met someone I enjoy spending time with and recently was told that my great grandfather and their biological great grandmother are brother and sister. I was devastated and was trying to figure out are we really genetically related and if so, what is the relationship.

    • http://www.joshuakennon.com/ Joshua Kennon

      That means your shared common ancestor is on the great-great grandparent level. You are 3rd cousins with only 0.781%, at most, shared genes. You are practically strangers. None of the 50 states even ban second cousins and you are even more distant that that – I know of nowhere in the world, throughout all of history, where such a congress would be forbidden.

      Frankly, I can’t name a single one of my third cousins and wouldn’t know them on the street if I met them. I imagine there are a significant amount of people in the United States married to their third cousin and don’t have a clue. This is not something that should cause you any emotional distress.

  • bianca

    Is the DNA percentage less for second cousins who share the same great grandmother but different great grandfather? would it be next to nothing? I apologize for my ignorance in advance.

    • http://www.joshuakennon.com/ Joshua Kennon

      Yes, the number would be cut in half as you only share a single common ancestor instead of two common ancestors. You’d only share a maximum of 1.5625% of your genes. There should be no issues with birth defects were such people to meet randomly, get married, and have a child, nor would such a union be prohibited anywhere on the planet to my knowledge.

      • kim

        I didn’t grow up with my boyfriend or know him
        but found out that my dad and his mom are 1st cousin s and we share the same great grandparents…..what are we 3rd cousins?

        • AntonDubinksy1960

          You are first cousins once removed, so share about 6% of the same genes.

        • PJ

          You are first cousin once removed to his mom and he the same to your dad. that makes the two of you as far apart genetically as second cousins, meaning you share about 3%

  • JD

    I don’t understand what they mean with “first once cousin removed” or “second cousin once removed”. Why does removed mean there? Why remove them?
    I would appreciate if someone could explain please. Thanks very much.

    • JD

      apparently I made typo: I meant: “first cousin once removed” and what does “removed” mean there? and the rest of the questions…
      Thanks very much for your help.

      • Frank

        Weird English family member classification that basically

        screws up anything to do with generation. Without the removed and stuff basically your father’s cousin is your cousin too……

    • qreusgurl .

      Removed means your cousin’s children. It’s just a simpler way of saying they’re not as closely related. It can get confusing.

      • Welbru

        No, it can also be your cousin’s parents. It means a generation up or down.
        In my family we call cousins once removed up ‘uncles’ and ‘aunts’ even though they’re not direct uncles and aunts.

  • Brad

    I was adopted at 3 days, I know my mother, I think I know my father, Could I DNA test my possible sister’s daughter and match to mine to see if we match. (Sister would have different mother). Would it be enough DNA match to see if I am part of that family?

    • JD

      why not compare your DNA with possible half sister then you get better results to show you are or not part of that family. There should be about 25% match between you and her. With her daughter the percentage obviously would go down more to 12.5% match or even less I think…

      Best wishes…

  • Libby Hanna

    i’m a double cousin, mums brother married dads sister, its super interesting to know how genetically similar I am to my cousins!!!!

  • kristy

    Why would there not be a 50% in the mothers box that makes no sense to me

    • Frank

      Assuming either parent is the same? Duh?

  • Tom

    In the context of us sharing 96% of our genes with chimpanzees how does this chart make sense? Do I share more genes with a chimp than my sister?

    • Caihlyn

      100% of your genes are from ‘humans’. 50% of your genes are from a specific human being, your mother and the other 50% are from a specific human being, your father. You are 100% made of human genes. Chimps share 96% of the same genes as ‘humans’ … not a percentage of a specific human being’s genes.

  • Dave Stupple

    Surely this is not right. My sister and I both got 50% of our DNA from our mother and 50% from our father. But we almost certainly did not inherit an identical 50% from each, so I do not have 50% DNA in common with my sister. The common DNA down the bloodline is always going to be lower than these figures, isn’t it?

  • William_JD

    None of this analysis works. Parents share almost all of their genetic material. If not, they couldn’t produce offspring with each other. The amount of shared genetic material among siblings (or cousins or whatever) will vary depending on the relatedness of the relevant ancestors and random chance in how the genetic cards are dealt.

    • Nathan

      Let me take a stab and guess you didn’t do so hot in your science classes? The analysis is correct. Borrow a high school genetics textbook and check the index for autosomal DNA consanguity. The layout might change but they all have the same information because that information is accurate. It shows the average contribution from each ancestor assuming no intermixing of the family tree for several generations to avoid more complicated calculations such as double cousins being as related as half siblings.

    • Sardeth42

      ..? I don’t follow?

      These are just statistical probabilities. Within a few generations other (healthy-normal) factors aren’t going to be enough of an influence…
      The more people you tested this the more accurate the numbers would become. ‘Tis the nature of statistics…

      ^None of this should have seemed unclear.

      Of 46 Chromosomes your parents each have each single sperm and egg only carries 23.

      Additionally of these chromosomes they are broken apart and recombine together in a (most likely) different manner…

      Whilst we might share the vast majority of our DNA with most every other human on this planet, their are different alleles.

      These are averages that are given presuming otherwise unrelated people; and as we know everyone is related somehow, but this shouldn’t even be an issue as after consecutive generations because presuming no major irregularities,

      AI would only share less than 0.00001% gene-similarity with any one of my Great*18—Grandparents (That would be a “level 20″ ancestor of mine)
      And I would have 1,048,576 Great*18—Grandparents under the atypical model provided here, but honestly even if you adjust those numbers either way by an ‘order’ of 15 it’s still going to be less than 5%…

  • me

    So my dad has two cousins who are married. The other one is his paternal cousin and the other one is his maternal cousin, so they’re not related to each other, but both are his cousins. Their children are my double second cousins or what? What would the percentage be?

  • Mike

    Ok I’m the father of two girls I just took a DNA test on my oldest she is not mine The weird thing about on the test it says shared alleles I’m 16 of 23 with that many matches I would think that I would be the father but I’m not here’s the question could it be one of my brothers or even how about my father

  • SJ

    I know normal siblings are ~50% similar in DNA makeup. What would the percentage be if their parents were first cousins? ~75%?

    On a side note: I only received 19% DNA from my paternal grandmother. I know it should be ~25%. What is the variance extremes that others have seen? Thanks!

  • Karen J. Harrington

    What is the percentage of DNA I would share with my half-sibling’s daughter? I am female, half-sibling is male. He is 10 years my senior; his daughter is 12 years my junior. Half-brother and I have same birth mother.

    • Welbru

      She’s your half niece, so wouldn’t you just halve the percentage for a full niece? I don’t thin gender or age would have anything to do with it.

    • Beetlejuice118

      Tell me that wasn’t a serious question lol

    • Beetlejuice118

      Sex and age have nothing to do with the gene you share with relatives (if you don’t count the X chromosome men receive from their mothers, which is about as significant as a drop of water in a pool). Age will never have ANYTHING to do with ANYTHING. You share roughly 50% of your genes with your full-sibling. If it’s your half-brother you share half of the genes you and a full-sibling would share (which is 50%). So you and your half-brother share about 25% of your genetic material. When he has a child, you will share half the genes with his kid as you did with him. So you will share 12.5% with your half-brother’s daughter (the same amount first cousins share).

  • Sassy lou

    All my husband wants to know is how much for his sperm? He has delta 32!!!

  • BarbB

    It sounds to me as if your parents are not very nice people and you don’t want to be like them. Your genetic makeup is not your destiny. Your height is a trait that is highly determined by your genes, but whether or not you are kind is something you have a high degree of control over.

  • Brilliand

    Don’t be careless with infinity, man. The number of possible gene combinations is indeed vast, but you cannot get infinity by multiplying finite numbers.

    The author of the article you linked did the same thing calculators tend to do in that situation – “The number’s too big, I quit.”

  • JustTellMeWhy

    Joshua, this chart is great, it’s exactly what I was looking for! Now, I know this article is a few years old, but hopefully you’re still responding to comments. I recently signed up for a DNA testing website, and they told me that I shared %0.92 DNA with somebody. I’m just wondering what math formula I could use to figure out what my possible relationship is to this person. Any ideas?

  • vermontsilkie

    Thanks for this chart. Even my college genetics professor couldn’t explain when I asked how much DNA I would share (on a statistical basis) with double second cousins. (Grandmother’s brother married Grandfather’s sister). Your chart makes it clear.

    Now a question: I have a brother with whom I share 44% DNA instead of the expected 50%. I realize that’s enough shared to rule out a NPE which we didn’t think anyway. Plus I obviously can’t share the Y chromosome. But still… are you just doing the mathematics or do you understand from a genetics point of view how that happens?

    • vermontsilkie

      To partially answer my own question – this kind of statistic is an area my reasonably recent genetics course did not cover – I am picturing my parents with two copies of each chromosome (each with its many genes). I know each will pass only one from each set down to me, and with a bit of luck I will end up with a full set of matching pairs but one from each parent. (And yes, I know it is actually more complicated than that considering there is also recombination in the mix.) Now the same two parents create another child. But Mom’s egg is a different one, with a randomly different set of her genes, that being again, just one from each of her pairs. Same with Dad’s sperm. Statistically that next child should get 50% of the same genes I got but *WAIT* not necessarily exactly. Theoretically the genes could be all exactly the same or all completely different but except for identical twins which is not the same as division of the already-fertilized ovum occurs, it just doesn’t happen. So really, sharing only 44.2% with my full brother isn’t that unexpected. I am female so we already know one chromosome I don’t share, the Y. We could have the same X chromosome or not. And so it goes.

  • Атул Кумар

    Then why some article say we share
    98 % with Chimpanzee
    85 % Zebra fish
    36 % Fruit fly
    Are they even closer than relatives ? 😛