How Many Ancestors Share Our DNA?

This post was written four years ago, using a quick-and-dirty model of recombination to answer the question in the title. Since then a more detailed and rigorously tested model has been developed by Graham Coop and colleagues to answer this same question. You can read more about the results of this model on the Coop Lab blog here and here. Graham’s model is based on more accurate data, more careful tracking of multiple ancestors and a more realistic model of per-chromosome recombination, and thus his results should be considered to have superseded mine.

Over at the Genetic Genealogist, Blaine Bettinger has a Q&A post up about the difference between a genetic tree and a genealogical tree. The destinction is that your genealogical tree is the family tree of all your ancestors, but your genetic tree only contains those ancestors that actually left DNA to you. Just by chance, an individual may not leave any DNA to a distance descendant (like a great-great-great-grandchild), and as a result they would not appear on their descendant’s genetic tree, even though they are definitely their genealogical ancestor.

At the end of his post, Blaine asks a couple of questions that he would like to be able to answer in the future;

  • At 10 generations, I have approximately 1024 ancestors (although I know there is some overlap). How many of these ancestors are part of my Genetic Tree? Is it a very small number? A surprisingly large number?
  • What percentage, on average, of an individual’s genealogical tree at X generations is part of their genetic tree?

I think that I can answer those questions, or at least predict what the answers will be, using what we already know about sexual reproduction.

Simulating Sex with Recombination

We can give a simple answer by assuming that each chromosome is passed on intact, with a 50% chance of getting either one from a pair. This gives us a maximum of 44 genetic ancestors, and means that the probability of being related to any particular ancestor N generations ago is 1 – (1 – 0.5N – 1)22. We’d have about 43 genetic ancestors out of 1024 genealogical ancestors after 10 generations.

This is an underestimate; outside of the Y chromosome and the mitochondria, DNA is not passed down as whole chromosomes; recombination occurs, in which chromosomes come together and swap DNA. This mixes up DNA and stop is getting lost, and lets you have DNA from more than 44 genetic ancestors.

To answer Blaine’s two questions, we need to take recombination into account. To do this, I put together a computer simulation of recombination, using data from Chowdhury et al‘s large population study of recombination; they found that recombination rates vary from person to person, and especially between genders, with significantly more recombination in women than in men (see this graph for the data I used). I simulation individuals with the 22 non-sex chromosomes, and each person had their own recombination rate, chosen at random, dependent on their gender. I simulated sexual reproduction with unrelated individuals, and checked whether their DNA was present in their descendants N generations in the future.

The results

Here are the results of the simulation:


This graph shows the probability that an ancestor of mine from N generations ago will pass DNA onto me, i.e. the probability that a genealogical ancestor is also a genetic ancestor. The black line is the simulation with recombination, the red line is our prediction without recombination; as we guessed, recombination increases your chance of being genetically related to your ancestors, though it still drops of pretty dramatically; after 10 generations, only about 12% of your genealogical tree is in your genetic tree.

The probability of having DNA from all of your genealogical ancestors at a particular generation becomes vanishingly small very rapidly; there is a 99.6% chance that you will have DNA from all of your 16 great-great grandparents, only a 54% of sharing DNA with all 32 of your G-G-G grandparents, and a 0.01% chance for your 64 G-G-G-G grandparents. You only have to go back 5 generations for genealogical relatives to start dropping off your DNA tree.

We also care about how many genetic ancestors we have after a certain number of generations, shown below:


The number of genetic ancestors starts off growing exponentially, but eventually flattens out to around 125 (at 10 generations, 120 of your 1024 genealogical ancestors are genetic ancestors).

As a final note, there is an interesting effect of the larger recombination rate in women; you are, on average, slightly more closely related to your maternal line (your maternal grandmother, your mother’s maternal grandmother, etc) than you are to you paternal line (your father’s paternal grandfather, etc). We can see the sharing probability for the maternal line and the paternal line show:


You are about 30% more likely to be genetically related to your maternal-line ancestor 10 generations ago than you are the corresponding paternal-line ancestor (14% vs 11%).

My not-very-well-documented R code for this simulation can be found here

Share and Enjoy:
  • Digg
  • Reddit
  • StumbleUpon
  • Facebook
  • Twitter
  • Google Bookmarks
  • FriendFeed

54 Responses to How Many Ancestors Share Our DNA?

  1. Harold Diamond

    Good day everybody, This is my testimony on how i won $326 million dollars on Mega millions lottery. I want to use this opportunity to thank Great Priest Essyewa for casting winning spell for me to win the lottery of $326 million lottery ticket. I have been playing lotteries for the past 5 years now and i have never won any. Ever since then i have not been able to win any lotto and i was so upset and i needed help to win this mega million lottery. so i decided to go online and search for help, there i saw so many good testimony about this man called Great Priest Essyewa of how he has cast lucky spell lotto for people to win the lottery. I contacted him also and tell him i want to win the Mega millions lottery, he cast a spell for me which i use to play and won $326 million dollars in mega millions lottery. I am so grateful to this man, just in-case you also need him to help you win, you can contact him through his email: and he will surely help you just the way he has helped me. i will forever be grateful to him and always testify the good work of him to the hole world. contact him via: and he will surely help you to win any kind of lottery

    Best Regard
    Harold Diamond

  2. On Tuesday, 29 September 2015 09:52:59 UTC-4, elizabeth henderson wrote:am elizabeth from UK I want to use this opportunity to sharing this great testimonies with you to all the viewers in the world, The best thing that has ever happened in my life is how i win the lottery. I am a woman who believe that one day i will win the lottery.finally my dreams came through when i email dr. clement and tell him i need the lottery numbers. i have come a long way spending money on ticket just to make sure i win. But i never know that winning was so easy until the day i meant the spell caster online which so many people has talked about that he is very great in casting lottery spell, so i decide to give it a try.I contacted this man and he did a spell and he gave me the winning lottery numbers. But believe me when the d raws were out i was among winners. i win $15 million. dr.clement truly you are the best, with these man you can will millions of money through lottery. so contact him if you want to winning this same way i win,is email or call via +254704881207

  3. Sandra Jason

    Hmm My name is Sandra Jason From USA I want to say I am the happiest person on earth today because My five years run away lover came back to me on his knees with tears on his eye begging me to forgive him and accept him back, DR AKERECO a great Spell caster made this possible with the help of a spell. i saw his email on the internet where a girl post on how DR AKERECO helped her so i decided to contact him and he told me that everything will be fine and now i am happy because DR AKERECO is a man of his word because everything went well as he promised me. Are you have misunderstanding with your lover, You need lottery spell, pregnant spell, or is your lover seeing someone else? what is your problem that you wish to solve? contact DR AKERECO his website is today and everything will be fine

  4. My name is Jessica Tom, From Germany.. My world and my life is back!!! After two year of Broken relationship, my boyfriend left me for know reason. I felt like my life was about to end i almost committed suicide, i was emotionally down for a very long time. (Thanks to a spell caster called Dr Onima), which i met online. On one faithful day, as I was browsing through the internet,I came across allot of testimonies about this particular spell caster. Some people testified that he brought their Ex lover back, some testified that he restores womb,cure cancer,and other sickness, some testified that he can cast a spell to stop divorce and so on. i also come across one particular testimony,it was about a woman called Jennifer,she testified about how he brought back her Ex lover in less than two days, and at the end of her testimony she dropped Dr Onima e-mail address. After reading all these,I decided to give it a try.I contacted him via email and explained my problem to him, he told me In 48hours my husband will came back to me. to my surprise he come to my house asking me to forgive him We solved our issues, and we are even happier than before Dr Onima, is really a gifted man and i will not stop publishing him because he is a wonderful man… If you have a problem and you are looking for a real and genuine spell caster to solve all your problems for you. Angain his email address is

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>