The first time Taosheng Huang saw the test results, it was certainly an error. Even after the repeated technical diagnostic, Huang does not believe. "This is impossible," he said.
Huang, and ġenetista pediatrician at the Medical Center & # 39; the Children's Hospital & # 39; Cincinnati, asked the patient to re & # 39; back and provide fresh samples & # 39; blood, Huang then divided among several laboratories & # 39; research to reduce any chance of & # 39; error. It was a finding that Huang knew it broke a key principle of human genetics – but time and time again, the result was the same.
The patient & # 39; Huang, child & # 39; four & # 39; years, was carrying two different sets of & # 39; Mitochondrial DNA: one mother, as expected another, from his father.
This was just the beginning. Through modern technology & # 39; DNA sequencing, Huang and his colleagues checked b & # 39; conclusively way mitochondrial DNA Windfall b & # 39; paternal way in & # 39; 17 individual cover three non-families related. Their work appears today in the journal PNAS.
"This is truly innovative discovery", says Wang Xinnan, biologist at the University & # 39; Stanford to study the mitochondria but was not involved in the new findings. "Can & # 39; opens up a whole new field … and change how you look the cause of & # 39; [certain] "Illness.
B & # 39; In general, we have a genetic mix & # 39; Mom and Dad. In the center, which our chromosomes, it is true. But the core is not the only part of the cell that contains the DNA. The cells contain power centers called mitochondria also carry their own DNA and almost all known animals, the mitochondrial DNA is inherited exclusively from the mother. This lopsided acquisition is so strong that researchers & # 39; often analyze the mitochondrial DNA to trace maternal linġenji back in time.
Scientists are still not completely sure why this process has evolved to strictly matrilineali, but few theories come from & # 39; before. For one, the mitochondria of & # 39; sperm are seen experiencing rates & # 39; Mutant higher than in eggs, and b & # 39; so their income is a little risky. In addition, having one type of & # 39; mitochondria make it easier for genome in the nucleus and mitochondria to coordinate, because both generate the raw material needed for proper cellular function, explains Sophie Breton, mitochondrial ġenetista at the University & # 39; Montreal who did not participate in the study. Adding & # 39; Mitochondrial other stakeholders, so the theory goes, you & # 39; distort this intimate dialogue with & # 39; both directions.
Whatever the driving maternal mitochondrial inheritance, it is clear that our cells have taken some precautions to keep it that way. formidable engine & # 39; molecular machines is ready to ensure that no undesirable parental input into the process of & # 39; fertilization. Even if the mitochondria & # 39; sperm helping white in its power, its mitochondria is not meant to last. Some mitokondri are considered lost as developing sperm; the few who make it through the process & # 39; fertilization are tagged with & # 39; chemical marker that allows the eggs and stop easily recognize any parental rogue interlopers.
A few animals, including flies and mice, are known to sometimes "leak" the mitochondrial DNA pattern in pups with maternal contribution, but humans have historically been excluded from this club. Only a few reports & # 39; mitochondrial DNA derived from existing dad, and most were calculated to contamination or mix & # 39; laboratory samples. One case, described in 2002, has received considerable attention when it was confirmed independently by a group & # 39; other research. But in the 16 years since then, the search for another example & # 39; this genetic anomaly failed.
So even after Huang was convinced that his remarkable patient & # 39; four & # 39; wireta years was the mitochondrial DNA from both parents, he knew that the work was far from done. When the researchers following this marked genetic signature fardja back in the family tree of the child, found that, over three generations, 10 individuals in the patient's family appeared to have mitochondrial DNA mixed. Now researchers knew x & # 39; and were seeking work & # 39; should look as extended their search. Not long after, seven & # 39; additional individuals from two other unrelated families were confirmed to have the same condition.
Amazingly, all three families appeared to show similar patterns & # 39; legacy & # 39; this unusual feature. Not all members were affected, which means that some individuals have passed their genes with typical fashion, and knew children who just inherited mitochondrial DNA & # 39; their mothers. But it was clear that the mitochondrial genome of & # 39; & # 39 several men in, these families were breaking the rules of biological paternity. Instead of disposable, these parents packages & # 39; genetic information in & # 39; any way kept pace with their maternal counterparts during fertilization, and left to some of their kids with mixed mitochondria .
Girls & # 39; these mixed genome then went on their heterogeneous voice on their own children b & # 39; carbon copy. This meant that their children inherited mixing indirectly – although the children had no mitochondrial DNA & # 39; own father. This was the case with the original patient & # 39; four & # 39; year & # 39; Huang.
Those who got mixed mitochondrial genome presented a somewhat more complex picture. The ability to pass the DNA side seems to be a dominant feature, or one that requires a gene from only one parent to show himself in the offspring. This meant that some of the men who inherited mitochondrial genome hybrids were able to transfer them to their children, who showed even more diversity by stirring the gene & # 39; Dad to Mom. But not all men with & # 39; mixtures maintained this capability, and led to occasional tips.
exactly and the mitochondrial DNA pattern infiltrate the embryo is not yet fully clear. It is definitely a genetic trait – but not one, ironically, found in the mitochondrial genome itself. In fact, besides the way & # 39; unusual heritage, there seems to be some flaws present in & # 39; some mitochondria & # 39; these patients. Instead, it is x & # 39; is the dads who deposit their mitochondrial DNA to their offspring x & # 39; mutation likely encoded in the nucleus – where things are properly coming both from mom and dad.
Florence Marlow, biologist development in the School of Medicine & # 39; & # 39 in Icahn, Mont Sinai who was not involved in the research, teorizza the anomaly can & # 39; is the step where the mitochondria of sperm is usually marked for destruction. If this step & # 39; never occur labeling, explains that eggs fertilized m & # 39; has no way to identify and eliminate these father interlopers, and means that the mitochondria of -Dad get clear step to proceed with the mother.
Since joining their initial findings, Huang and his team have already identified several other candidates with families & # 39; DM mitochondrial mixed. According to its preliminary estimates, this phenomenon can & # 39; & # 39 at present, more than 1 in 5,000 people. While Wang emphasizes that more research from other groups is needed to confirm these numbers, the work of the team & # 39; Huang indicates that transmission of mitochondrial father can & # 39; is much more widespread than when researchers think.
So how was ignored for so long? "The majority of people have taken for granted that mitochondrial inheritance is strictly maternally, 'Breton explains. "But the sequencing techniques are much more b & # 39; healthier than they were just a few years ago."
The possibility of & # 39; paternal heritage can & # 39; also expand our options for assisted reproductive technology in the distant future. The group & # 39; Huang had previously participated in the conception and delivery b & # 39; success & # 39; baby "three parents" in 2016. The child's mother suffered from mitochondrial disease, so Huang and his colleagues transferred its nuclear DNA in & # 39; donor bread, which was stripped of its own genome but can & # 39; providing mitochondria b & # 39; her health. This hybrid eggs, containing the genetic information from two mothers, was then fertilized with the sperm father.
In theory, Woods says, if the paternal mitochondria viable, can be added to & # 39 ;, or perhaps even replace, defective maternal mitochondria, and avoid the need for a third parent.
But that's a big if, especially considering that the mitochondrial DNA of & # 39; sperm is more prone to mutation. We & # 39; away to understand the full implications of & # 39; mitochondria with parents inherited in & # 39; natural circumstances, and much less by & # 39; artificial medical procedures, many of which x & # 39; likely to escape ongoing debates on ethics.
For now, the maternal inheritance of mitochondrial DNA is still the norm. But simply expanding our view of the genetic heritage open many doors. "These results will transform the way we describe the mitochondrial inheritance", says Breton. "I'm 100 percent sure that we will find more such cases in the future."