How Much Does Each Parent Contribute To A Child's Genetic Makeup

by Marina Watanabe
figures past Elayne Fivenson

Hours after giving nascency, my sister sent a pic of her newborn babe to our family group text. In what I can only presume was a painkiller-induced haze, she wrote, "The baby looks exactly like me!!!"

The babe did not expect exactly like her.

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

This idea of children being "mini mes" of their biological parents is a common conversation slice, and people oftentimes joke that the kid is a clone of i parent or the other. Despite these jokes, information technology's generally understood that information technology takes two to make a baby ( for the well-nigh part!! ) and that one-half the baby'south DNA comes from an egg and half from a sperm. But sometimes, a real "mini me" is built-in with the majority of Deoxyribonucleic acid coming from only one parent.

Family unit 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 marker the child as being peculiarly 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'southward 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 merely the begetter had the mutation. Before things could derail into a confusing and seemingly incommunicable game of "Who's the Mommy?!," the doctors did further genetic testing to reach a jarring determination: The patient'due south DNA was almost exclusively from the male parent. Also, I forgot to mention–the patient is a girl.

How we inherit genetic textile from our biological parents

Dna is the instruction manual of what makes you who you are, and information technology is constitute in your trunk in the form of 23 pairs of chromosomes (for a full of 46 chromosomes). Y'all got one set of 23 chromosomes from one parent inside a sperm, and the other 23 from the other parent within an egg. Because nosotros have 2 copies of our DNA, humans are what's known as "diploid" and this is annotated every bit "2n." Almost all the cells in your body comprise 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 but 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 developed male or female is very straightforward (Figure one). For each chromosome, y'all start with the total set consisting of 2 copies—one from each parent. Through a process called meiosis , these two chromosomes duplicate themselves (so y'all cease up with four copies of each chromosome) and ultimately split into four gametes containing just 1 of each chromosome–pregnant each gamete contains only half the corporeality 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 textile 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 germination. Parent ane (blue cells) and Parent 2 (red cells) both start with a complete pair of chromosomes (2n), duplicate their chromosomes (4n), and eventually end upwardly with iv gametes that incorporate half the normal number of chromosomes (1n). When two 1n gametes from ii different individuals combine together, a zygote (2n) is formed. For simplicity's sake, simply one ready of chromosomes is depicted, but this normally takes place beyond all 23 pairs of chromosomes simultaneously.

Redefining unmarried parenting

In the case of the nine year old daughter, she did not receive the normal one-half and one-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-broad 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 about all chromosomes from one parent. In this way, one person is essentially both biological "mother" and "begetter" to a kid. This is an incredibly rare status, and every bit of 2018, only approximately 21 cases accept been reported .

A curious feature of GWUPD is the fact that all of the patients affected are girls and women who have inherited by and large their father's genetic material. The reason why the unmarried genetic parent has thus far e'er been the father is non notwithstanding known due to the fact that the status is so rare and information technology is experimentally difficult to understand a process that is taking place in the very early zygote.

Though scientists withal do not fully sympathize GWUPD or its causes, they do have a theory . They believe that, much similar in classical zygote formation (Figure 1), a sperm and egg met to class a zygote. At this signal, both the Deoxyribonucleic acid from the sperm and the DNA from the egg should have begun replicating themselves so that the i-celled zygote could begin making more and more cells with both sets of Dna in order to create a fully-operation human embryo (Effigy 2a). However in the case of GWUPD, for any reason, the genetic information from the mother did not replicate properly, leading to two populations of cells–those with Deoxyribonucleic acid from both parents and those with Dna merely from the father (Effigy 2b).

*Figure 2:* Zygote replication. A) In classical evolution, the genetic source material from both parents are faithfully replicated and all resulting cells that will brand up the embryo take Deoxyribonucleic acid from both parents. B) In GWUPD patients, it is theorized that the genetic cloth 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 data volition undergo a process known equally "haploid rescue." This procedure is truly as dramatic and heroic as information technology sounds and consists of the paternal DNA replicating itself to go from being a 1n cell to 2n. For simplicity'south sake, only one set of chromosomes is depicted, just this process normally takes place across all 23 pairs of chromosomes simultaneously.

In GWUPD patients, these different cells with unlike chromosomes go on to etch different parts of the body so that, depending on the tissue, the genetics may vary. For instance, in the case of the nine year old Czech girl, the per centum of cells containing simply her father'south Dna was 93% in her claret just 74% in her saliva. So while she is mostly equanimous of her father'due south genetic material, she does still have some of her mother in her.

Side effects may vary

GWUPD patients frequently have loftier levels of insulin, asymmetrical body parts, seizures, severe developmental delays, are built-in 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 1 to the other and their symptoms vary. One of the reasons why the case of the Czech girl was and so interesting to doctors was the fact that she did non present with most of these common symptoms, but instead exhibited simply deafness and asymmetric legs. Although they followed her for three years (publishing the paper almost her when she was eleven), her doctors were unable to determine the cause of her deafness.

Stranger than fiction

We sometimes assume that creating a human being life is a elementary and straightforward process. Nonetheless, when we meet patients with GWUPD, nosotros empathize just how hands the procedure of creating new life tin can go amiss. The creation of a daughter from merely a human's genetic information sounds like something from Scientific discipline Fiction (and has actually been the footing for an episode of Physician Who !), but it is a phenomenon that very much exists and can take very negative consequences. While we may joke that a child is their parent's "mini-me," it is interesting to annotation that this is an actual possibility in the world of biological science. Having "too much" Dna from one parent might not seem similar a trouble in and of itself, just it is proof that genetic variety is of import for life.

*Effigy 3:* All babies look the same. Me (left) and my niece (correct) at roughly the aforementioned age. These photos evidence my completely informed and wise stance that all babies expect like potatoes (and thereby each other??) but probably non their parents. Haters gonna detest. 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 3rd-year Ph.D. student in the Biological and Biomedical Sciences programme at Harvard Medical School, where she is studying the genetics and biochemistry of the bacterial prison cell envelope

Encompass image: "Karyotype of a human male"

For More Information:

Read near this interesting example 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 calibration where only one chromosome pair or part of a chromosome pair comes from i parent. This is very different from GWUPD where well-nigh all of the chromosomes come from one parent.
See this Khan Academy page for an introduction to classical genetics and inheritance .
This Khan University link covers meiosis and how information technology leads to genetic diverseness. Lessons on this page explain a procedure called "recombination" that ensures genetic diversity in offspring. Recombination explains why siblings are genetically unlike from each other even though they share the aforementioned parental "source fabric" and why GWUPD patients cannot be regarded as clones of their fathers.