Genetic inheritance - Working backward in time

  1. Genetic inheritance - Working backward in time

    This is a very theoretical question.

    In theory, if everyone agreed and we DNA tested all 7 billion people on the planet today, could we mathematically work backward to figure out the EXACT DNA code of all our past relatives?

    So in theory, pretend we don't have a DNA sample from any of my past relatives, could we predict with 100% certainty what the DNA code of my dead father, or grand father, or great grand father, or great great grand father, etc, etc, would be? Would this be 100% accurate?

    In theory, all 7 billion of us must have a common ancestor, the theoretical Adam and Eve. Even if Adam and Eve never existed, we all still had to pass through a very small population of people.

    In theory, how far back could we predict just through DNA testing all 7 billion people today?

    {Lets assume that the DNA samples we take today would be the full 3.2 billion lines of code. And lets assume there are zero mistakes, zero error}
  2. jcsd
  3. Your assumptions are badly flawed. The DNA in our population is constantly changing due to mutations and recombination. These are being worked upon by the ever changing forces of natural selection -- at least in the active portion of your DNA -- so there is no way to reconstruct the DNA in the past with the DNA today. However, you can reconstruct phylogenies by noting where mutations have occurred in the inactive portion of the DNA (the vast majority) since these portions are not acted upon by natural selection.
    Also at least Eve did exist. By looking at the mitochondria in cells, we can see that every woman is descended from a single woman a long time ago.
  4. Hi MathAmateur,
    That's right, we know there must be a Mitochondrial Eve going back through the female line. In theory, ignoring mutations for a moment, Mitochondrial Eve would never change.

    We have a similar situation with Y-chromosomal Adam;

    But inside my cells, i have 23 pairs of chromosomes, that's 46 chromosomes, so that is 92 half chromosomes, i'm not sure if we could technically call them RNA's. Either way, i have 92 half chromosomes that MUST be copies of bits of other relatives of mine that lived in my past. If i only go back one generation, i have exactly half of my father's genes, and i have a quarter of my grand fathers genes, and one 8th of my great grand fathers genes.

    Now if i DNA test a large enough sample of the population, lets say all 7 billion people on the planet, in theory, i should be able to recompile my great grand fathers DNA code? Is that correct? I'm not sure?

    Me, the person i am today, is a combination of 92 half chromosomes, or 92 bits of other people.

    Last edited: Nov 8, 2012
  5. Monique

    Monique 4,445
    Staff Emeritus
    Science Advisor
    Gold Member

    Why do you come up with a theory when just yesterday you've stated that you don't know anything about inheritance?

    Your theory and stated 'facts' are incorrect, I suggest you first understand the basics of genetics before going any step further.
  6. Ryan_m_b

    Staff: Mentor

    It's not true that all women descended from a single woman, it's more complex than that. Mitochondrial DNA is only passed through the maternal line but the fact that there is a mirochondrial Eve (a women from whom all mitochondrial DNA is descended) does not mean that we did not descend from other women at the time. Think of it this way: would it be fair to say that I am descended from a single woman two generations above me? No, because my mother had a mother and my father had a mother. But I've only inherited my mother's mother's mitochondrial DNA. It's the same with mitochondrial Eve, there would have been plenty of women alive at the same time to whom we are all descended from but over generations all of Eve's female descendants turned out to be the ones who passed on their mitochondrial DNA.

    To the OP you really should try to learn about a subject before making theories on it. Even discounting mutation it is impossible even in theory to take my DNA and my sister's DNA and rebuild my mother or father and they are only one step away from us on a family tree. As has been explained in your other thread DNA inheritance works by essentially transferring a random half of each parents genome to the child. The chances of my sister getting precisely the opposite half that I received is astronomical, even if we take into account that >99% of our genomes will be identical because we are the same species.
  7. The reason i ask is that i was wondering if, in theory, without digging up dead bodies from the ground to get a DNA sample, could we work out the DNA code for famous people in human history? Maybe even clone them?

    Yes, i admit i know little or nothing about genetic inheritance, this why i am asking the questions.

    Could we, in theory, work out the DNA code of people like;
    Henry VIII of England;
    Galileo Galilei
    Christopher Columbus

    Could we work out the DNA code of people if we don't have their body any more?

    Imagine if we could clone famous people from human history? Its a cool thought!

  8. Ryan_m_b

    Staff: Mentor

    Cloning people would give you nothing more than a mostly identical twin. Due to epigenetics and differences in environmental exposure you are not going to end up with the same person. Do you understand my point above about why not even me and my sister could recreate our parents?
  9. Ryan,
    No, i don't understand Genetic inheritance and at this moment in time, i don't have the time to study it. But i do accept your word. If your adamant that its not possible to work backward through the generations to work out someone's DNA, then i take your word for it. If its not possible, then its not possible, i accept that!

    But you got to admit, its an intriguing thought to clone people who lived hundreds of years, or thousands of years ago, do you agree?

    Then there is the possibility of cloning someone who we can get a sample from by digging up the body. We actually have the bodies of Henry VIII of England, Galileo Galilei and Christopher Columbus. We could dig them up and see if we could extract a DNA sample to clone them. Or even someone who died more recently, like Elvis. There must be intact bone marrow still in the bones of Elvis, he's not dead that long.

  10. Ygggdrasil

    Ygggdrasil 1,820
    Science Advisor

    The idea you propose is close to what some scientists have done. By looking at the DNA sequences of genes from existing organisms, scientists can use computational methods to trace backwards through evolution and infer the most likely sequence from the common ancestors of those organisms. These methods of ancestral gene reconstruction rely on a number of assumptions (and work better for some applications than others) but have led to a number of very important findings in evolutionary biology. For a good, general audience piece on the subject see For a technical review of the subject see

    As for the question you asked, I would say no (unless you relax the 100% certainty criteria). For example, consider the simpler problem of reconstructing an individual's genome from the sequences of that individual's children. Each child will have 50% of the individual's genome, and the portion of the genome that each child inherits is randomly selected. Therefore, on average, individuals with two children will pass only 75% of their DNA to their offspring and 25% of their genome will not be represented in their children. In order to reconstruct 99% of an individual's genome from that individual's children, that individual would have needed to have had 7 children. Even at 99% sampling, we would still lack information about 30 million base pairs of the individual's DNA. Of course the problem is made simpler by the fact that all human sequences are extremely similar, but the sampling problem will be very real for individuals who had no or very few offspring.
  11. Evo

    Staff: Mentor

    You do realize that cloning them would only produce a person that looked like them. The person would have none of their memories, knowledge, etc.. They would not grow up as the same person.
  12. Ygggdrasil,
    Thank you, some good links!

    Yes, that's very interesting what you say about sampling 7 children might give you roughly 99% of the parents DNA code. If we expand that theory to its limit, lets say a couple have 30 children, and we get the DNA code of the children, we would still never reach the full 100% of the parents DNA code by examining the children's DNA. With 30 children, we might get 99.9999% of the parents code, but never 100%. We would never get the exact code of the parent, we would always fall short.

    So the real answer to my question is that with a massive sample of DNA from the human population, we could get close to predicting the code for people in the past, but we could never get it 100% accurate. At least not without a body with intact DNA in the bone marrow. We would need a dead body, and the body would have to be reasonably well preserved to get a usable sample. Its a bit like what the Japanese scientists are trying to do to get a DNA sample from a dead Woolly mammoth, in an attempt to clone the Woolly mammoth and bring the species back to life. The Japanese scientists say they might be able to do this within a few years.

  13. Evo,
    This is not true! Yes, your right that the cloned person would have no memory of its past life. But the clone would be 100% identical in every way. It would be a 100% perfect identical twin in every way, less the memory and environmental effects.

    Lets use Elvis as an example;
    If we cloned Elvis, the clone would be 100% identical to the original Elvis, but without the past memory and past environment. The cloned Elvis would lead a completely new life from start to finish. The cloned Elvis would look identical to the original Elvis, in every way. The cloned Elvis might turn out to be fatter, or thinner. He might be richer or poorer. He might get an incredible education, or he might get a bad education. Or he might even be raised in a different country and speak a different language the second time.

    But the cloned Elvis would have all the identical personality traits of the first Elvis. We know the original Elvis was an incredible singer. So the cloned Elvis would also have the potential to be an incredible singer, if someone teaches him. If Elvis has a "joyful" personality, then the clone will have this personality trait. If Elvis picked his nose a lot the first time around, then the cloned Elvis will likely have the tendency to pick his nose. Regardless of the environment the cloned Elvis is raised, all the same personality traits will re-appear.

    Its like people always say about their children - "Like father, like son", or "She is just like her mother". Except with a clone, the coincidence's would be uncanny because they would be so similar to the original person.

  14. Monique

    Monique 4,445
    Staff Emeritus
    Science Advisor
    Gold Member

    Not true. Even identical twins are not genetically identical:

    The genetic contribution does play a large role in development of a personality, shown by studies on identical twins raised apart (
  15. Monique,
    The article says they did tests on 19 sets of "identical twins" and showed their DNA was not identical. I assume all the twins were teenagers or adults. So maybe we accumulate many more breaks and mends in our DNA as we progress through life, creating slight changes in the code sequence. Its a psychological argument about personality differences. Different people will draw different conclusions.

    Either way, its difficult to prove. You would have to DNA test all the twins at birth and then test them again when they are adults to see how many differences we accumulate during our life.

    The original Elvis was an incredible singer, the whole world loved him. I'm quite confident that a cloned Elvis would also be capable of singing incredible songs, if someone teaches him.

    There is another brand new factor here in human cloning, and its this - Lets say we clone Elvis the singer. Yes, the cloned Elvis will lead a completely new life. But!! People will know "who" the cloned Elvis really is, or was, in his past life. And because everyone will know who he was in his previous life, people will start teaching the cloned Elvis to sing at a very early stage because they know what he should be capable of. As the cloned Elvis goes through his new life, people will teach him about his previous life, they will show him films he stared in and they will play him his own music he wrote. The cloned Elvis will become very famous, and he might, or might not, choose to play along and repeat what he did the first time.

    Hmmmmmm..... come to think about it, sounds a lot like reincarnation that the Buddhists talk about or the rebirth spoken about by Jesus in Christian Bible.... LOL :biggrin:

  16. Monique

    Monique 4,445
    Staff Emeritus
    Science Advisor
    Gold Member

    That's the point, after the first embryonic cell division the two daughter cells are already different. The idea that one could clone a person that is "100% identical in every way" is flawed. The idea of a "100% perfect identical twin" is flawed as well, as shown in the article.
  17. Yea, maybe!

    I still think digging up the dead body of Elvis Presley, taking a DNA sample, and cloning him, will give us a person with all the personality traits of the first Elvis. There are several million people who would love to hear Elvis sing again .....LOL

  18. Ryan_m_b

    Staff: Mentor

    Identical twins, and therefore clones, do not have identical bodies and the genetic link to peso alert is tenuous at best. A cloned elvis would have:

    - different uterus environment
    - different nutrition/exercise during upbringing
    - different life experiences that play a significant role in personality
    - different education (life education as well as academic) leading to different interests and opinions.

    You are not going to get an elvis mark two. At best you will get someone that, I pressured and trained, may be a descent elvis impersonator but otherwise they are a completely different person.
  19. Ryan,
    I'm sorry, i dispute that! I think your wrong.

    Yes, if the cloned Elvis never hears about his first life, and the cloned Elvis is, lets say is raised in Bangladesh, India, on the edge of a poverty stricken dump, yes, the cloned Elvis will turn out very different! Capable of singing but maybe nobody would ever notice. In theory, he could end up different if he is raised in a different country in different circumstances.

    But in all probability, that is unlikely to happen. In all probability, if we did clone Elvis, it would be his living descendent's in the USA today that would clone him. It would be his children, grand children, or great grand children that would give the legal consent to clone Elvis. And Its his living descendants that would have to provide a female volunteer to carry the cloned Elvis child for 9 months through to full term and birth. In effect, one of Elvis's female children or grand children would be carrying their own grand father in their womb. Sounds funny doesn't it, that a child might end up carrying their own cloned parent for 9 months in the womb. But that is what would happen. If there is no female descendant, then some other close female descendant who is related to Elvis would have to volunteer to carry the child. There would be plenty female volunteers willing to carry the cloned Elvis for 9 months!

    Then it would be Elvis's grand children that would raise the cloned Elvis as a child. Its his own family descendants that would nurture him, and teach him his values in life. And its his grand children that would inevitably teach the cloned Elvis to sing again. They would teach him about his past life when he is young. And by the time the cloned Elvis is 20 years of age, every TV station in America, and around the world, would want him to sing on TV shows. And i seriously doubt that the cloned Elvis would reject the fame and fortune that comes with being associated with his past life. He would love the fame just as much as he did the first time!

    So in reality, you would not be able to tell the difference between the original Elvis and the newly cloned Elvis. Even if the cloned Elvis had different personality traits, because of the fame and fortune, he would learn to act out the role he played the first time. He would learn the personality of the person he was the first time. he would learn to develop that deep voice again!

    I mean think about it - If you thought you could earn the fame and fortune that Elvis did, you too would learn to sing and play that role in life. I would do it anyway.

    Last edited: Nov 9, 2012
  20. Evo

    Staff: Mentor

    This is ridiculous. trolololol
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