by Marina Watanabe
figures by Elayne Fivenson

Hours after giving birth, my sister sent a picture of her newborn baby to our family group text. In what I can only assume was a painkiller-induced haze, she wrote, “The baby looks exactly like me!!!”

The baby did not look exactly like her.

The baby, like all newborn babies, looked exactly like a potato.

This idea of children being “mini mes” of their biological parents is a common conversation piece, and people often joke that the child is a clone of one parent or the other. Despite these jokes, it’s generally understood that it takes two to make a baby (for the most part!!) and that half the baby’s DNA comes from an egg and half from a sperm. But sometimes, a real “mini me” is born with the majority of DNA coming from only one parent.

Family matters

In the Czech Republic, a deaf nine year old child underwent genetic testing to try to pinpoint the cause of the deafness. Apart from the length and width of the patient’s legs slightly differing, there were no features to mark the child as being particularly out of the ordinary. The genetic testing results showed that the patient had two copies of a specific mutation, or alteration, in the genetic code. Interestingly, though, the mutation in question was not thought to cause deafness. 

To begin unraveling the mystery of the relationship between the mutation and the patient’s deafness, the doctors tracked the mutation within the family. Classical genetics states that since the patient had two mutant copies of the gene, both parents must also have the mutation and they both must have passed it onto their child. The parents underwent genetic testing and it was determined in a bizarre twist that only the father had the mutation. Before things could derail into a confusing and seemingly impossible game of “Who’s the Mommy?!,” the doctors did further genetic testing to reach a jarring conclusion: The patient’s DNA was almost exclusively from the father. Also, I forgot to mention–the patient is a girl.

How we inherit genetic material from our biological parents  

DNA is the instruction manual of what makes you who you are, and it is found in your body in the form of 23 pairs of chromosomes (for a total of 46 chromosomes). You got one set of 23 chromosomes from one parent inside a sperm, and the other 23 from the other parent inside an egg. Because we have two copies of our DNA, humans are what’s known as “diploid” and this is annotated as “2n.”  Almost all the cells in your body contain a copy of this full set of 23 pairs of chromosomes you got from your biological parents. The exception are gametes, which are sex cells (sperm or eggs), that only contain 23 chromosomes—not 46. Since they only contain one copy of our genetic information, gametes are 1n instead of 2n. 

 Normally, the creation of gametes in an adult male or female is very straightforward (Figure 1).  For each chromosome, you start with the full set consisting of two copies—one from each parent.  Through a process called meiosis, these two chromosomes duplicate themselves (so you end up with four copies of each chromosome) and ultimately split into four gametes containing only one of each chromosome–meaning each gamete contains only half the amount of DNA required for a human. This “halving” process occurs simultaneously across all 46 chromosomes, leading to the production of many gametes containing 23 chromosomes each. After meiosis, a sperm and an egg are then free to combine their incomplete genetic material to create a genetically complete cell known as a zygote. This single-celled zygote is what grows into a new human.

Figure 1: Classical gamete formation. Parent 1 (blue cells) and Parent 2 (red cells) both start with a complete pair of chromosomes (2n), duplicate their chromosomes (4n), and eventually end up with four gametes that contain half the normal number of chromosomes (1n). When two 1n gametes from two different individuals combine together, a zygote (2n) is formed. For simplicity’s sake, only one set of chromosomes is depicted, but this normally takes place across all 23 pairs of chromosomes simultaneously.

Redefining single parenting 

In the case of the nine year old girl, she did not receive the normal half and half ratio of DNA from her parents. Though the doctors were trying to diagnose the cause of her deafness, they instead diagnosed her with genome-wide uniparental disomy or diploidy (GWUPD). In this condition, a person will not inherit 23 chromosomes from one parent each for a total of 46, but will instead inherit almost all chromosomes from one parent. In this way, one person is essentially both biological “mother” and “father” to a child. This is an incredibly rare condition, and as of 2018, only approximately 21 cases have been reported

A curious feature of GWUPD is the fact that all of the patients affected are girls and women who have inherited mostly their father’s genetic material. The reason why the single genetic parent has thus far always been the father is not yet known due to the fact that the condition is so rare and it is experimentally difficult to understand a process that is taking place in the very early zygote. 

Though scientists still do not fully understand GWUPD or its causes, they do have a theory. They believe that, much like in classical zygote formation (Figure 1), a sperm and egg met to form a zygote. At this point, both the DNA from the sperm and the DNA from the egg should have begun replicating themselves so that the one-celled zygote could begin making more and more cells with both sets of DNA in order to create a fully-functioning human embryo (Figure 2a). However in the case of GWUPD, for whatever reason, the genetic information from the mother did not replicate properly, leading to two populations of cells–those with DNA from both parents and those with DNA only from the father (Figure 2b). 

Figure 2: Zygote replication. A) In classical development, the genetic source material from both parents are faithfully replicated and all resulting cells that will make up the embryo have DNA from both parents. B) In GWUPD patients, it is theorized that the genetic material from the egg does not replicate. Thus, resulting cells may or may not contain maternal DNA. In those 1n cells that only contain one copy of paternal DNA, the lonely genetic information will undergo a process known as “haploid rescue.” This process is truly as dramatic and heroic as it sounds and consists of the paternal DNA replicating itself to go from being a 1n cell to 2n. For simplicity’s sake, only one set of chromosomes is depicted, but this process normally takes place across all 23 pairs of chromosomes simultaneously.

In GWUPD patients, these different cells with different chromosomes go on to compose different parts of the body so that, depending on the tissue, the genetics may vary. For example, in the case of the nine year old Czech girl, the percentage of cells containing only her father’s DNA was 93% in her blood but 74% in her saliva. So while she is mostly composed of her father’s genetic material, she does still have some of her mother in her. 

Side effects may vary 

GWUPD patients often have high levels of insulin, asymmetrical body parts, seizures, severe developmental delays, are born prematurely, and/or are more susceptible to developing cancer. Since each patient derives their DNA from their individual and unique parent, the genetics of the patients vary wildly from one to the other and their symptoms vary. One of the reasons why the case of the Czech girl was so interesting to doctors was the fact that she did not present with most of these common symptoms, but instead exhibited only deafness and asymmetric legs. Although they followed her for three years (publishing the paper about her when she was 11), her doctors were unable to determine the cause of her deafness.

Stranger than fiction

We sometimes assume that creating a human life is a simple and straightforward process. However, when we see patients with GWUPD, we understand just how easily the process of creating new life can go awry. The creation of a daughter from just a man’s genetic information sounds like something from Science Fiction (and has actually been the basis for an episode of Doctor Who!), but it is a phenomenon that very much exists and can have very negative consequences. While we may joke that a child is their parent’s “mini-me,” it is interesting to note that this is an actual possibility in the world of biology. Having “too much” DNA from one parent might not seem like a problem in and of itself, but it is proof that genetic diversity is important for life.   

Figure 3: All babies look the same. Me (left) and my niece (right) at roughly the same age. These photos prove my completely informed and wise stance that all babies look like potatoes (and thereby each other??) but probably not their parents. Haters gonna hate. Potatoes gonna potate.

Marina Watanabe is a PhD candidate in the Biological and Biomedical Sciences graduate program at Harvard University. She loves her potato niece very much.

Elayne Fivenson is a third-year Ph.D. student in the Biological and Biomedical Sciences program at Harvard Medical School, where she is studying the genetics and biochemistry of the bacterial cell envelope

Cover image: “Karyotype of a human male”

For More Information:

  • Read about this interesting case of a patient with mostly maternal DNA who has cells that are XX (biologically female) or XY (biologically male) depending on where they are sampled from. 
  • Uniparental disomy is GWUPD on a small scale where only one chromosome pair or part of a chromosome pair comes from one parent. This is very different from GWUPD where almost all of the chromosomes come from one parent.
  • See this Khan Academy page for an introduction to classical genetics and inheritance
  • This Khan Academy link covers meiosis and how it leads to genetic diversity. Lessons on this page explain a process called “recombination” that ensures genetic diversity in offspring. Recombination explains why siblings are genetically different from each other even though they share the same parental “source material” and why GWUPD patients cannot be regarded as clones of their fathers.

12 thoughts on “I Didn’t Get It from My Mama: Children with DNA almost exclusively from their dads

  1. Thank you for this very interesting contribution!
    I did not know the phenomenon of GWUPD. I do know and agree, all newborns are potatoes.
    Best wishes and good luck for your further research!
    Victoria (University Diderot, Paris)

  2. It is nature finding a way… Nature always finds a way…. For years we have been hearing about the Y chromosome disappearing and thus the spike in female births….. Well… This is nature working out the equation to keep things flowing. . I bet these girls born with mostly their fathers genes will only produce male children and these male children will have non depleted Y chromosomes….

    1. I didnt know anything about disappearing or depleted y chromosomes.
      I understood that certain stresses upon the mother prior to or during conception wood make it difficult for the embryo to be conceived as or matured into a male and wonder if some females or hermaphrodites have at least some xy chromosomes that were inadequately nurtured (or-not to equate the two- feminized) by some process during embryonic development or if conversely some hermaphrodites or males have xx chromosomes but were hyper-masculinized by an analogous but masculinizing process

    2. That’s not how it works. The father determines the gender of the baby. The woman can ONLY donate an X chromosome. If a girl with GWUPD isn’t sterile, she would have the exact same chances of having a son as any other woman.

  3. Hello, Just wondering if a child gets both parent’s surname with their own name?? Coz in our culture it’s often said that a child continues the generation of father side, so gets father’s surname only,but what about mother who nourishes him/herin hercwomb for 9months and goes thru all the physical pains and sometimes social stress to produce a Male child,and when the baby comes to the world gets father’s name tag.what about mother??I cant get an answer.

  4. it’s very interesting, knowing such a
    rare cases, specially for me as as biological educator graduate, but what i observed is prior to the diagram provided is that, if the maternal chromosome didn’t function of recombine with the paternal DNA, then how did the girl still have a mother’s gene? (93% from the blood & only 74 from saliva are from his father) 😅?

    1. Hi Mark,
      Good question. Although the answer to your question is not known for sure, one theory is that the maternal chromosomes were present in the single-celled zygote, but the mother’s chromosomes failed to replicate as they should have. This caused an imbalanced distribution of chromosomes as that single cell become 2, then 4, then 8, and so on, with some cells harboring only dad’s DNA, and other cells harboring DNA from both parents. During development, these imbalanced cells began developing into all of the various cell/tissue types that make up the body, distributing themselves throughout the developing human. In the case described here, it seems that more of the “dad-only” cells ended up composing the blood, where as more of the “dad + mom” cells were found in the saliva. finally, in terms of your question about recombination, it appears that none occurred during meiosis (presumably because the maternal chromosomes failed to replicate, if the theory is correct).

  5. It is very interesting and knowing such as , one theory is that the maternal chromosomes were present in the single-celled zygote.

  6. Thank you for your very interesting article. My husband is of white, English origin, with dark brown hair and blue eyes, whilst I am of Indian origin with black hair, dark brown eyes, mid brown skin colour and distinctive sharp features.

    This area has fascinated me, as neither of our two children (girls) look anything like me. They are almost carbon copies of eachother (even though they are 12 years apart in age) and they both look incredibly like their dad.

    The only real difference between them is that our eldest has slightly darker eyes, hair and skin. She has hazel eyes, but the youngest has bright blue eyes. So, we were thinking that I must have an ancestor who had blue eyes (as unlikely as it seems). Our youngest daughter also has a line running down from the centre of her neck and down her chest and back, where she is darker on one side of her body and noticeably lighter on the other side. This is replicated in her hair, which is a mid brown all over, but on the half of her body that is lighter, she has a distinctive blond streak running through her hair.

    We have heard of situations where a mother was carrying twins and one embryo assimilates with the other and ends up being the only child, but carries the genetics of 2 different people inside them. We thought this may have happened with our youngest daughter. However, reading your article, I am now thinking that may be my genes did not divide properly and so both our daughters took many more chromosomes from their father, explaining why they look nothing like me and why our youngest has this ‘split’ colouring. It doesn’t bother us at all, in fact we find it quite fascinating. But, from a future health and interest point of view, it would be good to know what might have been going on.

    I know you can’t say anything for sure, but from your research and experience, what would be your thoughts in this situation?

    Thank you for reading and I look forward to hopefully hearing from you.

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