Summary: In 3 cases, Mitochondrial DNA from the father has been passed on to the child.
Maybe this happens a lot more often than documented. In this case, it can throw the field of mtDNA testing and implications into question.
Conversely, maybe it happens extremely rarely and only in pathological cases (in the mathematics/statistics sense, if not the medical sense). In this case, it's just a medical curiosity and only important insofar as a doctor treating a patient with a rare disease may want to consider the remote possibility of this.
It wasn't entirely clear how strongly this would invalidate conclusions drawn from a belief it was matrilinial descent only. For instance, is this enough to totally wreck the single-eve hypothesis? Or, change some of the patterns of human dispersion models? Or the neanderthal-sapiens crossbreeding?
Likely not since this still seems to be extremely rare and only happen when things don’t go according to plan at least in humans.
But it does indicate that more research is needed to understand the implications of this, especially on genetic screenings.
Also mitochondrial eve isn’t a hypothesis, but rather stub for the most recent common genetic ancestor of modern humans before the divergence of the mitochondrial DNA groups.
Also it’s important to note that mitochondrial eve isn’t a “fixed individual” in say 50,000 years the mitochondrial eve candidate would be shifted to someone who lived well pass the current one as lineages die out.
Also, the application of "mitochondrial" to the common female ancestor is somewhat spurious. There is a common male ancestor as well. And if mitochondria did not exist, there would still be a common female ancestor.
The mitochondria connection is just that it's a tool that can be used to estimate the time and location of that ancestor. She would not have been the only human alive at that time and there was nothing special about her mitochondria.
No, there’s not necessarily a single common female human ancestor. There might be several of related, but not reliably interfertile, species. The most recent common ancestor in that case might be quite nonhuman, though presumably a primate.
I think that the boundary case is that we at least have a common ancestral single cellular life-form. To my mathematically inclined approach, anything else (such as a the earliest common ancestor being close-to-human, or whether there needs to be a male or female one) is not a logical debate, but rather a biological investigation.
> I think that the boundary case is that we at least have a common ancestral single cellular life-form.
It is possible to imagine several different single cells being our ancestore. If we pretend a lightning strike in the ancestor primordial DNA soup sparked life, then it could have sparked life in millions of cells with a single lightning bolt.
There could even have been several different puddles of DNA soup.
In theory it doesn’t, but because the effective population size of humans until recently has been very small, the probability is very high that the last common maternal ancestor lived relatively recently.
An interesting aside is everyone who lived more than 2000 years ago is either your ancestor or has no living descendant. This wasn’t true before 1803 because the Tasmanian aborigines had been genetically isolated since the end of the last ice age [0].
Yes and no. Just by the time you get back 2000 years you have so many ancestors that you are related to everybody alive. There are no isolated human populations so everybody is related to everyone else.
Actually you only have around 1000 effective ancestors from that time as you don't inherit DNA from every ancestor.
But I feel this logic completely ignores "inbreeding" even if it's to the 5th, 10th or 20th degree.
It's like seeing a human as the root of its ancestors tree, and saying that this tree is well balanced all the way to the nodes at depth 100 or so. But surely it's not a well balanced tree, more like a directed graph with many sideways connections. There could be multiple clusters, lineages, more or less narrow, coming from the bottom and reaching the top.
Yes this is true at the genealogy level, but because of the way meiosis works once you get back more than about 12 generation some of your ancestors don’t pass any of their DNA down to you.
Invalidating conclusions: not particularly; these results suggest that under rare circumstances (in a few sorts of mitochondrial disease), mitochondria can be transmitted paternally. It makes the matrilineal model slightly less definitive, but, overwhelming often, accurate (note that people with mitochondrial diseases rarely exhibit this feature, and are less likely to reproduce anyway due to the disease).
Single Eve: still holds; given the small population size of humans in the past, at some point there was a female ancestral to us all, as other lineages would have stochastically died out.
Human dispersal and Neanderthal-modern human crosses: both have been examined via autosomal DNA. Reconstructions of dispersal may be skewed in the following manner: since we use X- Y- and mtDNA to look as sex ratios of admixture events (such as in modern Caribbean populations, where there is more European male influence and African/Native American female contribution), our reconstruction may be skewed by these selection due to incompatibilities. We expect there to have been some incompatibilities between modern humans and Neanderthals/Denisovans—no doubt some were mitochondrial. But autosomal DNA bears the evidence of our admixture. Likely some lineages (including those with prehistoric-human mt- and Y-DNA) were lost, either due to selection, stochasticity, or likely, both.
Doesn’t the paper specifically say that they really have no idea of the impact because not enough attention has been paid to determine the amount of paternal inheritance? You sound awfully sure of yourself considering maternal inheritance of mtDNA has been practically gospel for 50 years.
I agree. I wouldn't rush to draw any conclusions, as this paper changes the status quo. We can not say anything about the rarity of transmission events in the past really. This work is focused particularly on heteroplasmy -- it doesn't rule out other causes.
It does not seem we understand the mitochondrial inheritance mechanism during conception.
We can set an upper bound on paternal mitochondrial inheritance: there are hundreds of thousands of mitochondria in an egg, and tens in a sperm.
If all paternal mitochondria were transferred every time (unlikely‡), then a child's mitochondria would be ~99.99% inherited through the mother.
‡ Unlikely because sperm mitochondria are located toward the flagellum in order to power locomotion, and the capsule at the head is normally the only part which fully penetrates the cell membrane.
Does that not assume that the mitochondrial from both parents are treated equally in terms of inheritance? It seems to me that biological systems do not tend to use random chance most of the times if there is a evolutionary benefit, thus if there is such benefit I would predict that those "tens" would be treated differently from those hundreds of thousands.
I was mostly talking about the concept of mitochondrial incompatibility, which is significantly more common than what is discussed in the paper, which is paternal inheritance. I made a note of it being doubly rare (female must survive to reproduce age with a specific mitochondrial sort of defect)
>these results suggest that under rare circumstances (in a few sorts of mitochondrial disease), mitochondria can be transmitted paternally.
"Although biparental inheritance of mtDNA and heteroplasmy coincided with disease symptoms in some of the individuals studied by Luo et al., the authors’ data do not demonstrate a causal link with disease. In fact, we cannot be certain that the study participants have mitochondrial disease, because no specific examinations to confirm this diagnosis are reported. Further study is needed to identify more cases of potential paternal mtDNA inheritance, and to determine the functional consequences of such heteroplasmy."
So no, it is not definitively linked with mitochondrial disease. If anything, the article suggests that the inheritance may be due to an abnormality in the host DNA:
"Previous work has shown that mitophagy, the process by which cells ‘eat’ their own mitochondria, has a role in the selective elimination of paternal mitochondria. Given our rapidly expanding knowledge of mammalian mitophagy in vivo16, these rare instances of paternal mtDNA transmission might be attributed to defective mitochondrial turnover. The inheritance pattern of paternal mtDNA in Luo and colleagues’ study suggests that a yet unidentified gene on one of the autosomes (non-sex chromosomes) is involved in eliminating paternal mitochondria."
These are good questions that will definitely need to provoke further investigation. They'd be out of the scope of this article because the news of paternal mtDNA transmission really is that fresh.
I'm curious about how often this happens across different species. Once we know that rate for mammals and/or specific species, for example, I wonder what effect(s) it would have on estimations of generations and evolution over time. Think about mitochondrial Eve for example.
The meme is in reference to this popular quote, not the other way around. The quote has been around since Philip Siekevitz published an article on this in 1957.
Maybe this happens a lot more often than documented. In this case, it can throw the field of mtDNA testing and implications into question.
Conversely, maybe it happens extremely rarely and only in pathological cases (in the mathematics/statistics sense, if not the medical sense). In this case, it's just a medical curiosity and only important insofar as a doctor treating a patient with a rare disease may want to consider the remote possibility of this.