
Mitochondrial DNA can come from both parents - rbanffy
https://arstechnica.com/science/2018/11/plot-twist-mitochondrial-dna-can-come-from-both-parents/
======
ghshephard
I'm not sure how much of a "plot twist" this is - when I took my biology
course _decades_ ago, it was explained to me that both maternal and paternal
mitochondria were passed on, but the Egg is so much larger than the sperm,
that the impact of of paternal mitochondria, and amount passed on, was
relatively minor. I guess the interesting detail here is that the amount
present raises to the level of catching a DNA scan.

~~~
ArchTypical
> I'm not sure how much of a "plot twist" this is

I was taught differently in 1998.

There was the press coverage of:
[https://en.wikipedia.org/wiki/Lucy_(Australopithecus)](https://en.wikipedia.org/wiki/Lucy_\(Australopithecus\))
which was referenced in a scene of
[https://www.imdb.com/title/tt2872732/](https://www.imdb.com/title/tt2872732/)

It can be said that it's a plot twist that was stoked for decades.

~~~
mbreese
I remember being taught that there was a paternal component of mtDNA, but that
the contribution was really small (<10%, maybe <1%). However, I don't remember
if this was undergrad (~ 1998) or grad (~2000)... probably grad school.

~~~
ArchTypical
> probably grad school.

I was an undergrad, which still puts us both above the vast majority in
education.

------
crusso
"It’s not clear why mtDNA prefers being exclusively maternal"

Wait... I thought that the reason mtDNA came from your mother is that the egg
from your mother forms your first cell and the sperm only delivers DNA into
the nucleus. They cytoplasm all comes from your mother. In that cytoplasm
swims your mother's mitochondria.

I assumed when I started reading this article that maybe somehow mitochondria
from the sperm sneaks out into the cytoplasm of your initial cell.

Is that understanding not correct?

------
pbhjpbhj
Aside: this question came to mind today, is there any discernible genetic
component from a surrogate mother (a womb donor, as it were)? It seems highly
likely to me _a priori_?

~~~
CWuestefeld
Certainly an epigenetic contribution. It turns out that the mother's body
during pregnancy can have a huge _and heritable_ impact on the baby. E.g.,
studies have shown that nutritional problems (like famine) during pregnancy
can cause the baby to have obesity problems later in life. These have been
shown to be the result not of direct genetics (the fetus's DNA has already
been selected), but by causing a different mix of genes to be _expressed_.

That shouldn't be too surprising. It seems logical that evolution would find a
way to prepare a baby to be born into an highly-food-constrained environment
so their metabolism will be more conserving of resources.

What really is surprising (at least to me) is that the child's propensity has
been observed to be passed down even to the grandchild.

------
bookofjoe
[http://www.pnas.org/content/early/2018/11/21/1810946115](http://www.pnas.org/content/early/2018/11/21/1810946115)

------
amelius
In the age of low-cost DNA sequencing, shouldn't this be simple to figure out?

~~~
inetknght
I work as a software developer at a DNA analysis company with an in-house lab.
You might be surprised to know how much knowledge is regurgitated and how
little actual research occurs.

~~~
kothar
I'm very interested in working in the genetics/biotech industry as a software
engineer - how much specialist knowledge do you feel is required to approach
that career path? My background is computer science, so I have been looking
around at biochemistry courses which might be helpful.

Would love to pick your brain if you have the time :)

~~~
inetknght
Specialist knowledge? I've never been to high school or college. I don't have
a degree. I've been writing software for 20 years but couldn't even spell the
words in DNA before I was hired.

It helps to have bio knowledge but biotech really just needs a lot more
software tools. There's a lot of low-hanging fruit for automation and
analysis. There's a hell of a lot of room for people smarter than me to
innovate.

There's a ton of room for improvement in the privacy area. You can read what
I'd said about that in previous [0] comments [1]. I very strongly disagree
with some types of industry standard software [11] [12]. They're highly
sensitive to input and timing and contribute to reproducibility problems in
the industry.

I think that's a problem which plagues the industry right now:
reproducibility. I can't speak for the UK (where your profile says you're
from) but in the USA the FDA (in charge of medicine) recently had a "truth
challenge" [3]. In it, participants were asked to analyse the same set DNA
data. Nobody got the same answer and very few even got _consistent_ answers
[4]. That's Very F@#$ing Scary if you ask me since the DNA data starts with
just text files [5] [6]. So irreproducibility of results is solely due to
poorly designed software (and I can discuss at length about that if you want).

If you want to stay in computer science, then tackle that. A lot of the
industry is based off of BWA [7] and GATK [8]. They're nowhere near as bad as
IMPUTE2 or Admixture, but they're highly sensitive to parameter changes (and
every analysis company uses different parameters). There are other open-source
analysis tools as well but they're nowhere near as popular. There's of course
not-so-open-source tools too which I don't feel like mentioning (I work on one
such software as an internal tool for the company).

On a different note, one of the problems that underpins this whole technology
is the way "Next Generation Sequencing" works: shear your DNA into small
fragments so that sequencing machines can analyse each fragment in parallel
(in contrast to linearly through the strand before it was cut up) [9]. Then
the software analysis tools try to re-assemble all those pieces back into a
single fragment.

If you were to take this comment and cut it up into words and sentence
fragments, would you be able to reassemble the words back into the correct
post? Of course not. So that's very much a limiting factor to analysis [10].

Realistically this forum is not ideal for communication. I looked at your
profile but did not see a way to contact you. But feel free to contact me at
the email in mine. I don't check it often though :)

[0]
[https://news.ycombinator.com/item?id=18196717](https://news.ycombinator.com/item?id=18196717)
[1]
[https://news.ycombinator.com/item?id=16754393](https://news.ycombinator.com/item?id=16754393)
[3]
[https://precision.fda.gov/challenges/truth](https://precision.fda.gov/challenges/truth)
[4] [https://precision.fda.gov/challenges/truth/results-
explore](https://precision.fda.gov/challenges/truth/results-explore) [5]
[https://en.wikipedia.org/wiki/FASTA_format](https://en.wikipedia.org/wiki/FASTA_format)
[6]
[https://en.wikipedia.org/wiki/FASTQ_format](https://en.wikipedia.org/wiki/FASTQ_format)
[7] [http://bio-bwa.sourceforge.net/](http://bio-bwa.sourceforge.net/) [8]
[https://software.broadinstitute.org/gatk/](https://software.broadinstitute.org/gatk/)
[9] [https://en.wikipedia.org/wiki/DNA_sequencing#High-
throughput...](https://en.wikipedia.org/wiki/DNA_sequencing#High-
throughput_sequencing_\(HTS\)_methods) [10]
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4531809/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4531809/)
[11]
[https://mathgen.stats.ox.ac.uk/impute/impute_v2.html](https://mathgen.stats.ox.ac.uk/impute/impute_v2.html)
[12]
[http://software.genetics.ucla.edu/admixture/](http://software.genetics.ucla.edu/admixture/)

~~~
kothar
Thanks! Excellent pointers, I had no idea the sequence fragments being aligned
were so short in some cases.

I can't see your email either, so I assume the profiles don't publish them.
You can reach me at mike at <username>.net however.

------
sigstoat
is there some website along the lines of "things you learned in <= freshman
university science class that has been updated"?

------
droithomme
This has been known for a long time. It's a myth that mtDNA only comes from
the mother and was based on a misreading of an old paper decades ago. I don't
know why the myth has so much traction among geneticists who should know
better. Many claims have been made deriving from these assumptions. Nearly all
research purporting to date past branches of populations based on mtDNA
mutations by assuming a maternal clone is passed, and any differences are
mutations, is completely off. All that research is and always has been
invalid.

1996 paper on paternal mtDNA inheritance:
[http://www.pnas.org/content/93/24/13859.full](http://www.pnas.org/content/93/24/13859.full)

2002 paper on paternal mtDNA inheritance:
[https://www.newscientist.com/article/dn2716-mitochondria-
can...](https://www.newscientist.com/article/dn2716-mitochondria-can-be-
inherited-from-both-parents/)

Wikipedia's been updating this article since 2006:
[https://en.wikipedia.org/wiki/Paternal_mtDNA_transmission](https://en.wikipedia.org/wiki/Paternal_mtDNA_transmission)

~~~
samatman
> Nearly all research purporting to date past branches of populations based on
> mtDNA mutations by assuming a maternal clone is passed, and any differences
> are mutations, is completely off. All that research is and always has been
> invalid.

This is a drastic and totally implausible statement that is not supported by
any serious geneticist, nor by the Wikipedia article you've linked to.

mtDNA does not have to come exclusively, 100%, no-exceptions-ever from the
mother, in order for population research which uses to be valid! 99% is quite
sufficient. It is at least 99.9% accurate: as the Wikipedia article helpfully
points out, there are 1000x as many mitochondria in an egg as in a sperm.

~~~
droithomme
You're attacking a strawman.

mtDNA can be used to track lineages. It's the dating of when branches occurred
that is off because it assumes all differences are due to mutations and not
paternal contributions.

~~~
gus_massa
I'd have to take a look at the details, but I'm 99% sure that the important
part is that the mitochondrial DNA has no crossover, so all the differences
are due to mutations and it is a real tree.

With normal DNA the crossover add some changes and in particular it mix the
changes in one branch of the tree with the changes in the other branch of the
tree, so it's not longer a tree.

So my guess is that it will not change the dates too much, specially since he
dates are calibrated by historical events. With made up numbers, something
like "we know that this population reach here 10000 years ago and has 37
changes and that population reach there 20000 years ago and has 69 changes.
This other population has 53 changes so after some complicated math, we
estimate that they split 15000-1600 years ago.

I guess that the size of the population at the bottlenecks will be slightly
reduced, because IIUC they are not calibrated using historical data but using
some mathematical models about how the size of the population affect the
diversity. I don't expect a big change nevertheless.

------
iscrewyou
Then this [1] article from 3 weeks ago now means that we can also get our
stresses from our mothers.

1\.
[https://news.ycombinator.com/item?id=18405636](https://news.ycombinator.com/item?id=18405636)

------
robsanchez1954
More info here:
[https://www.nejm.org/doi/full/10.1056/NEJMoa020350](https://www.nejm.org/doi/full/10.1056/NEJMoa020350)

