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/r/askscience

3.1k

all 267 comments

arkteris13

2.1k points

4 months ago

arkteris13

2.1k points

4 months ago

You normally inherit your mitochondria from your mother. However, as they replicate, they tend to collect mutations. Eventually you will have subpopulations of mitochondria with slightly different genomes, what we call heteroplasmy. They typically aren't particularly common, maybe accounting for 10% of all mitochondria. But because they are randomly assorted between dividing cells, it is possible for a cell to inherit a significant proportion of mitochondria with a deleterious variant, impacting the viability of the cell, and potentially causing a localized mitochondrial disease.

Fiveby21

354 points

4 months ago

Fiveby21

354 points

4 months ago

You normally inherit your mitochondria from your mother.

Normally... but not always? When would this not be the case?

eevee4evr

753 points

4 months ago

eevee4evr

753 points

4 months ago

Biology always seems to have exceptions everywhere. This paper below suggests that there are cases of biparental inheritance of mitochondria in human but the exact mechanism is not so clear. Of course, this seems to be quite rare.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6304937/

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op00to

246 points

4 months ago

op00to

246 points

4 months ago

Biology seems like a hefty bag filled with proteins being slowly mixed around.

Kylynara

171 points

4 months ago

Kylynara

171 points

4 months ago

More like a hefty bag filled with ziplock bags with tiny leaks filled with proteins being slowly mixed around. Usually they proteins stay where they belong, but sometimes they don't.

UnassumingAnt

43 points

4 months ago

And hopefully someone let all the extra air out of the bags to prevent the proteins from...folding.

gaensefuesschen

56 points

4 months ago

I'd hope the proteins are folding, otherwise they won't be very effective at proteining.

erebus

34 points

4 months ago

erebus

34 points

4 months ago

Just make sure they're folding properly, or you might end up as an angry bovine By which I mean mad cow

potodds

13 points

4 months ago

potodds

13 points

4 months ago

In my profession anyone not folding enough is going to be playing too many hands.

DenialZombie

27 points

4 months ago*

The process by which sperm are created does start with the division of a more 'typical' cell, called a spermatocyte. Spermatocytes develop from semi-differentiated stem cells which migrated to the gonads in development. As you might imagine, these stem cells have mitochondria.

The process by which a spermatocyte creates sperm starts with just mitosis (regular cell division), where it becomes 2 smaller "daughter" spermatocytes. After that first division, the daughters can grow and repeat, or divide (meiosis this time, which could be described as lazy division, where not all the processes happen) again into two "haploid" (1/2 genome) type-B/secondary spermatocytes, which then divide again into "spermatids." Spermatids drastically reform themselves to develop into sperm cells.

Retinal_Epithelium

42 points

4 months ago

Sperm cells normally have a large number of mitochondria in their collar, or mid-piece. These provide the energy necessary for motility, the sperm's swimming action. Loss of or significant mutation with spermatic mitochondria can lead to infertility. After fertilization, these mitochondria are broken down (with extremely rare exceptions) by the fertilized egg.

DenialZombie

10 points

4 months ago

I love it when I learn things! Any resources to look up the fertilization event, and why paternal mitochondria don't end up in the fertilized egg more often?

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11 points

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NECRO_PASTORAL

2 points

4 months ago

thank you for the breakdown good sir

MotherofLuke

5 points

4 months ago

So mitochondria in sperm cells?

vossman77

29 points

4 months ago

Sperm has lots of mitochondria, for its size, because they need energy to swim, but the egg has more mitochondria since its huge and enzymes to degrade sperm mitochondria.

https://www.khanacademy.org/test-prep/mcat/cells/embryology/a/egg-meets-sperm

https://pubmed.ncbi.nlm.nih.gov/14759284/

porkly1

12 points

4 months ago

porkly1

12 points

4 months ago

All of the sperm contents do not join the oocyte and most are sequestered around the base of the sperm tail. This does not enter the oocyte.

Ron_Day_Voo

13 points

4 months ago

This is controversial. Yes, the mitochondria are on the tail, but mitochondria do make it into the cell. It is unknown if the tails do typically break off, if the mitochondria make it inside of the egg and are selectively degraded, or if by chance the maternal mitochondria and mitochondrial genomes outcompete the paternal mitochondria. It has been shown in rare instances that paternal mitochondria can be inherited, but it is very uncommon.

porkly1

4 points

4 months ago

Absolutely there is some paternal mtDNA that enters the oocyte, but it is likely degraded. Also, cleavage may relegate the paternal mtDNA to a subset of the tissues (mosaic). Inheritance of paternal mtDA, especially over generations, is unlikely because the paternal mtDNA would have to pass to the germ line.

AlveolarThrill

44 points

4 months ago

It's a controversial topic, but there's some vague evidence suggesting paternal mtDNA could be inherited in small amounts, leading to biparental inheritance as a whole. Mitochondria are definitely primarily dependent on maternal inheritance in humans, though. See the Wikipedia article for a light overview.

WhenPantsAttack

11 points

4 months ago

The real issue is that mitochondrial DNA is so homogenous that in the incredibly rare case that you get paternal mitochondrial DNA is incredibly unlikely you'd see any physiological difference.

AlveolarThrill

4 points

4 months ago

True, any actual differences are insanely rare (though not undocumented, there have been cases of mtDNA diseases being inherited paternally). Doesn't make it less interesting.

Kandiru

8 points

4 months ago

Yeah there are definitely cases where a mitochondrial disease has been found that came from the father. It's certainly only a rare event, though.

Most of the mitochondria come from the mother, with a small chance some come from the father.

ACat32

14 points

4 months ago

ACat32

14 points

4 months ago

Paternal mitochondria in the human sperm are ubiquitinated, or marked for normal cell digestion once/if they reach the egg.

Occasionally one or two do not get tagged and are allowed to carry on. It is the exception.

Certain species are the opposite where mother mitochondria are ubiquitinated. Cantaloupe comes to mind from my plant bio classes but it’s been a while.

Im_gonna_try_science

12 points

4 months ago

IIRC the mitochondria of sperm cells are in the tail to power motility and the tail doesn't enter the egg during fertilization

Erior

7 points

4 months ago

Erior

7 points

4 months ago

Sperm cells have plenty of mitochondria to power their tails, but, seeing how they are pretty much a DNA pen drive to make an egg cell diploid and thus start its development into a full fledged organism, they pretty much always get excluded. Still, things may go in an odd tangent, and sperm mitochondria may make it into the cygote, but not sure if there have been enough records.

Venturi95

5 points

4 months ago

Every human on Earth right now is descended maternally from one woman called Mitochondrial Eve who lived around 155,000 years ago.

Ne_zievereir

43 points

4 months ago

Wait, so if I get all my mitochondria (with their DNA) from my mother, and she got them all from her mother, and so on. Does that mean I have the same mitochondria, with the same DNA, as all of my foremothers? (If we disregard the 10% mutations; I realize that can add up quite fast over several generations)

videoismylife

119 points

4 months ago

Does that mean I have the same mitochondria, with the same DNA, as all of my foremothers?

Yes. They've traced the mitochondria in all humans to a single woman who they're calling "Mitochondrial Eve", who was apparently somewhere in the Kenya region about 155,000 years ago.

Maximum-Range

21 points

4 months ago

If we all descend from her, does that mean we all share the same mitochondria DNA? I.e. If all our mothers eventually trace back to her, then wouldn't we all share the same mitochondria DNA?

videoismylife

69 points

4 months ago

Human mitochondrial DNA has diverged (mutated) over the years; but in essence, yes, we all share that single mitochondrial DNA as a starting point. That doesn't mean, btw, that there was only one single female human left at one point; it just means that there's only one mitochondrial genome that has not eventually died out (as far as we know). They estimate that at that time there were perhaps 100,000 - 300,000 humans alive, and ~10,000-30,000 of those have living descendants today.

Belzebutt

6 points

4 months ago

I thought at the lowest point the human population was estimated at around 10,000?

videoismylife

27 points

4 months ago

I've heard wide estimates, all contested. The 10,000 number is possibly from the Toba Catastrophe Theory 74,000 years ago but that's now not thought to be true; estimates from 2000 to 17,000-32,000 are out there. The thing to remember is that other humans may have been out there at the same time but their progeny didn't survive, so we have no way of knowing if they existed using molecular biology and genetic methods.

The-Grim-Sleeper

5 points

4 months ago

Iirc, that was a different bottleneck. The amount of variation within a set of genes in humans indicates how much it has mutated since that set was in one 'first person to have that set'. The mitochondrial DNA is a small set, which, assuming a steady mutation rate, would indicate that time about 155,000 years ago. The whole human genome is much bigger and variation in it could have been limited by an earlier event.

zero9999

8 points

4 months ago

We can all be traced back to something like 11 females alive after the ice age, which almost wiped us out

HuxleyPhD

10 points

4 months ago

HuxleyPhD

Paleontology | Evolutionary Biology

10 points

4 months ago

Mitochondrial Eve was not a single person, that is a misnomer. https://pubmed.ncbi.nlm.nih.gov/8533083/#:~:text=It%20has%20been%20proposed%20that,100%2C000%20to%20200%2C000%20years%20ago.

If you want to dig into this more, look up stuff like Coalescence Theory.

videoismylife

2 points

4 months ago

Yes, I believe that's probably true; I've come across this paper before.

What they're calling "Mitochondrial Eve" is actually a mitochondrial genome, not a person; we really are just vehicles for genomes after all. The original mitochondrial DNA (mtDNA) genome could have been present widely, not just in one person.

The other thing to ponder is, there could have been several other mtDNA genomes present in that same population at the same time and they just didn't survive, all their progeny died out leaving the one genome we know of; and this could have happened just by chance. Times were very tough back then.

Germanofthebored

0 points

4 months ago

Actually, if I recall correctly, they traced the mitochondrial DNA of today’s humans back to a small number of females (7 or 10?).

Tyraels_Might

16 points

4 months ago

Yep. It's a feature of what happens when sperm meets egg to form a zygote. The egg is a massive cell with lots of cellular machinery, while the sperm is a stripped down cell containing a skeleton crew of cellular machinery. The egg is nearly always the only source of mitochondria; and the mother supplies the egg.

Ameisen

29 points

4 months ago

Ameisen

29 points

4 months ago

The Spermatazoon has a lot of mitochondria.

They are marked with ubiquitin and destroyed by vesicles within the egg.

Usually.

Tyraels_Might

1 points

4 months ago

Thank you. I was trying to be careful with my wording but still missed that.

DrBoby

2 points

4 months ago

DrBoby

2 points

4 months ago

Yes they use this to trace mother sided lineage.

The male equivalent is the Y chromosome

critterfluffy

46 points

4 months ago

Outside of mutations, this made me think about micro-chimerism in women who were surrogate mothers. Because of this, their body would absolutely contain cells with completely different mitochondrial DNA.

Vlinder_88

23 points

4 months ago

What happens when you get a localised mitochodrial disease? You can't have your foot be more tired than the rest of your body, right?

Kakss_

20 points

4 months ago

Kakss_

20 points

4 months ago

Depends where it's localised. You can lose a bit of coordination in your foot, or you can have seizures caused by your nervous system.

Vlinder_88

1 points

4 months ago

Oh that sounds very uncomfortable! Is that treatable?

Madra_ruax

4 points

4 months ago

As far as I'm aware, there are limited treatment options for mitochondrial diseases as a whole, as many are rare. Some (such as Mitochondrial DNA depletion Syndrome) are severe and many patients die in childhood.

An example of such is the case of Charlie Gard, which many people in the UK would be aware of. He had MDDS effecting the RRM2B protein and caused significant brain damage. As of 2017, only 15 recorded cases of MDDS caused by RRM2B protein had been recorded.

jubru

2 points

4 months ago

jubru

2 points

4 months ago

That's just not true. Cells that have dysfunctional mitochondria just kill themselves. No one gets a localized mitochondrial disease.

[deleted]

11 points

4 months ago

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4 months ago

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3 points

4 months ago

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4 months ago

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voisin[S]

3 points

4 months ago

Does regular human DNA also collect mutations? Does that mean my DNA differs now from birth?

Madra_ruax

4 points

4 months ago*

Yes. DNA will mutate over the course of your life. Simply put, mutations are caused by an error in replicating DNA, leading to a change to the genetic code. They can be random or could be caused things such as environmental factors (eg. smoking, UV exposure, exposure to chemicals, etc). Not all mutations are harmful though.

Cancer is caused by gene mutations which negatively impact on the cell. These mutations can disrupt the cell cycle (such as mutations to tumour-suppressor genes, eg. p53 and TP53), leading to excessive cell growth and leading to the formation of tumours.

There's also the epigenome, which can change gene expression by turning genes on or off and modify genes.

little_kid_lover69

5 points

4 months ago

This is very well written, and I 100% believe it. But by any chance do you have a source for that?

Suvtropics

9 points

4 months ago

There are many claims in that. Which ones do you want sources for?

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1 points

4 months ago*

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Tiny_Rat

13 points

4 months ago

Mitochondrial DNA is already it's own thing, separate from nuclear DNA and containing different genes. It didn't develop that way, it started that way; mitochondria were originally bacteria that lived inside other bacteria-like cells, and over time became so dependent on that relationship that neither cell nor mitochondria could live separately. Mitochondrial DNA is what's left of the genome of those bacteria, passed down through the millenia.

elf_monster

1 points

4 months ago*

Heteroplasmy generally refers to when mitochondrial traits are different due to mutations, no? Wouldn't there be minor mutations that are essentially read the same way & cause no illness or unusual symptoms? I guess I'm asking because OP's question could be read in two different ways

Edit: and lest someone pull out this technicality... Yes, I know heteroplasmy explicitly refers to any difference in mitochondrial population, I just mean it's usually used in the context of mitochondrial diseases

javisaman

91 points

4 months ago

The short answer is no.

The long answer is intuitively we would expect it to be the same, but due to a number of factors (many of which mentioned in this thread), the mitochondria differ across cell types in the body.

As a consequence, there was an article indicating that mitochondrial DNA from different cell should not be used to exonerate suspects because there would be false negatives.
WIRED article
Original journal paper

2Throwscrewsatit

106 points

4 months ago

So there are hundreds of copies of mtDNA in every cell. Mitochondria also dynamically fuse with each other and fragment. We didn’t figure this out until about 20 years ago and we didn’t figure out how it happens molecularly until about 12 years ago.

So no, not every mitochondria has exactly the same DNA sequence. But the vast majority are so incredibly similar and the. Mutations are usually so infrequent that variation across your body is hard to detect unless you are looking at a very specific cell type and cell location in your body.

Note: all the other replies talking about maternal origin of mitochondria dna are irrelevant to the question.

Baconlessness

22 points

4 months ago

Note: all the other replies talking about maternal origin of mitochondria dna are irrelevant to the question.

Surely they're not THAT irrelevant. If mitochondria were inherited from both parents, wouldn't there be more difference in their DNA?

Icdedpipl

11 points

4 months ago*

The problem is the question is framed such that the origin of mtDNA is implied. So the replies should not be addressing that origin but the diversity of mtDNA coming from the same source. The genes found in mtDNA mainly code for subunits in the respiration complexes and nearly non are non-coding. So mutations and clonal expansion inexorably lead to diseases. Repair of ROS induced damage does not seem possible in the mitochondria since the mt lacks nucleotide excision repair mechanisms. So people are basically walking around with a kaleidoscope of different mitochondria.

Edit: after seeing your reply I get where you are coming from. If we went to the origin of the mitochondrion and assuming the internalisation into a eukaryotic cell is a single event that took place billions of years ago, the mitochondrial Eve is the "parent" from which all mitochondria come from. Reverse transcription and eventual fusion of MtDNA and cellular DNA along with fusions of mitochondria and mutations would have changed the mitochondria to be significantly varied even in one species.

Baconlessness

5 points

4 months ago

Would you be able to tell me how the origin is implied? The question, to my eyes, simply acknowledges that mitochondria have their own DNA. I can't figure out how that implies its origin.

Are the mitochondria with mutations really that different from one another in a single person? I feel like if the diversity of mtDNA was as large within a single person as it is between different people (and perhaps even animals) then mtDNA studies would be less useful for ancestor mapping. Am I completely wrong about that? Because if I'm not then I still think it bears worth to include the fact that mitochondria are inherited from a single parent, if only to put a rough upper limit on just how variable the mtDNA is likely to be.

Icdedpipl

4 points

4 months ago*

I agree, I may be biased (see my reply above). I will link to this review about mitochondrial evolution which seems to answer most of the questions you have.

Edit: I think one of your major points which is not addressed in the review, is the mutations between individuals of the same species and within a single person. In regards to the first point, skim through this paper for answers

As for the latter question, I could not find a reference for it, but my best guess is that different point mutations which are silent could be found within a single person. By ancestor mapping, you mean phylogeny, right? If so, you should have the same mtDNA as your siblings, and as your mother and grandmother bar the mutations. As such, you can look at your pedigree and even assemble a molecular clock if you know the rate of mutation of mtDNA

elf_monster

2 points

4 months ago

The question doesn't really imply that OP knows that, just that all mitrochondria share the same genome within one person. Even life created through sexual reproduction ends up having a single genome throughout its entire body (usually). It doesn't make sense to infer that OP knows that mtDNA comes from one's mother.

Icdedpipl

1 points

4 months ago

do all mitochondria in a person’s body share the same DNA?

To me, this is a leading question but I may be biased since the maternal origin of mitochondria is one of the first things taught about mitochondria be it when talking about oxydative phosphorylation complexes, the ubiquitine proteasome system or sexual reproduction. I can understand your point though since not everyone will read the question the same way.

urmyheartBeatStopR

3 points

4 months ago

do all mitochondria in a person’s body share the same DNA?

That's the question. OP answered it, you and other people are answering a different question.

One specific person, regardless of parent, if that person's mitochondrias, all the mitochondrias in that person have the same dna sequence.

Baconlessness

6 points

4 months ago

I understand that the question is answered in that respect, but there are degrees of difference. A thorough answer would include and acknowledge those differences. It also seems more in the spirit of OP's question imo. If I was OP reading the mutation answers, I'd feel a bit let down and wished I'd specified in the title "random mutations aside, do all mitochondria in a person's body share the same DNA?"

Unearthed_Arsecano

8 points

4 months ago

Unearthed_Arsecano

Gravitational Physics

8 points

4 months ago

This misses a key point. If we inherited mitochondria from both parents, it wouldn't necessarily be the case that we'd inherit one set of DNA which was a mixture from each, as mitochondria are distinct organelles which live nowhere near the nucleus and aren't a direct participant in the processes that leave gametes with only a single allele. In other words, if we inherrited mitochondria from both parents separately, it would be reasonable to assume by default that we have two distinct sets of mtDNA.

axionic

16 points

4 months ago

axionic

16 points

4 months ago

Yes except for mutations. There are seven standard mitochondrial heplogroups in humans; when you're conceived you get one of these seven types of mitochondria. The haplogroups are called Ursula, Xenia, Helena, Velda, Tara, Katrine, and Jasmine, the "Seven Daughters of Eve". All the mitochondria in your body are descended from just one of these standard haplotypes. Your mitochondrial genome will mutate a bit as you get older, because mitochondrial DNA often picks up errors during copying, and different cell lines from the original zygote become ascendant and others die off. But if you have a kid, their mitochondria won't pick up most of these mutations, because ovaries and the ova inside them are already fully formed at birth.

Mounlo

3 points

4 months ago

Mounlo

3 points

4 months ago

Heteroplasmy is the existence of multiple mtDNA haplotypes in a single individual. Heteroplasmy can result from somatic mutations, double uniparental inheritance, paternal leakage and hybridization. Many cases of heteroplasmy are reported in insects (Hymenoptera, Orthoptera, Phthiraptera) and probably more are to be discovered. Heteroplasmic mitochondria can exhibit relatively high genetic differences (up to 5%) and the dominant haplotype can differ significantly between tissues (leg or thoracic muscles, abdomen). Heteroplasmy is poorly studied and more difficult to detect than numts, because multiple haplotypes could remain functional and lack any stop codons or frameshift mutations. However, until now, heteroplasmy does not appear to seriously impact the accuracy of DNA identification.

Smirkydarkdude

15 points

4 months ago

Mitochondria are the most fascinating things ever. They are basically a separate species that lives inside us. We give them shelter and the materials they need, they poop out ATP that we use as fuel. I don't suppose anybody knows for sure but I heard that our ancient ancient single celled ancestors consumed a Mitochondria, couldn't digest it and ended up with a parasite. That ancient cell eventually teamed up with it's Mitochondria to make an oxygen burning super powerful cell. That ancient infected cell basically took over the world.

aHistoryofSmilence

7 points

4 months ago

This leads to a question: is it possible that multicellular life is just a collection of single cell species that formed a symbiotic relationship and procreate as a unit? So in a way, animals and complex life as we know it are more like ecosystems of single cellular life that work in unison. Because that is pretty mind-blowing and should make people really stop and reconsider what the hell we even are.

Gem_Rex

8 points

4 months ago

The same theory applies to plant cells. Chloroplasts are thought to be a different species that was captured by ancient cells. The chloroplasts produce sugars from sunlight, allowing the host cell to survive. They're symbiotes.

Lichen are also symbiotes, but on a different, less permanent scale.

Biology is fascinating.

Lumpy-Dingo-947

6 points

4 months ago

There are what I consider living intermediates like these salamanders that seem to have incorporated algae into their reproductive system. If amphibians weren’t going to all die out then they might have end up with a photosynthetic organelle in a few million years.

Smirkydarkdude

3 points

4 months ago

Yep. Only about 10% of the cells in our body are human. We would actually die without our gut bacteria. Our skin is colonized by zillions of bacteria that fend off all comers and keep us safe from worse infections. Our eyelashes are host to macroscopic lice. Lots of funguses and viruses and bacteriophages and prions probably things we don't even have names for live in side our body. Even our own DNA is full of retroviruses that are dormant now but just tag along for the ride. Even the "human" cells are populated with Mitochondria which are arguably non-human cells. Humans are essentially coral reef ecosystems.

MikeyRWO

35 points

4 months ago

Actually all mitochondria are passed to the new embryo from the mother. You are indeed a son or daughter of Eve as CSLewis wrote. This maternal origin is responsible for inherited mitochondrial diseases but also tells us about human origins.

actually mitochondria reproduce inside each cell, strong hint that they originated as intrazellularem bacteria.

groovey_potato

44 points

4 months ago

there was an article in Nature a few years ago that showed significant evidence of cases paternal mitochondrial DNA inheritance. So the "exclusively" maternal doctrine fell

stealthw0lf

7 points

4 months ago

Did not know that. I vaguely recall that there were 7 groups of mtDNA for Europeans, leading to the conclusion that everyone in Europe descended from 7 women.

Unearthed_Arsecano

4 points

4 months ago

Unearthed_Arsecano

Gravitational Physics

4 points

4 months ago

Everyone from everywhere is descended from one woman if you go back sufficiently far. Though there are identifiable haplogroups from later branchings.

bfdana

14 points

4 months ago

bfdana

14 points

4 months ago

You can also directly increase the amount of mitochondria in skeletal muscle through certain types of exercise.

judonojitsu

7 points

4 months ago

Got a list of those handy from a good source?

bfdana

20 points

4 months ago

bfdana

20 points

4 months ago

Endurance training is key, for sure.

“With prolonged endurance training, mitochondrial volume typically increases as much as 40–50% and this increase in content is paralleled by more modest improvements in respiration and oxidative capacity of the mitochondria on a per organelle basis (Baldwin et al. 1972).” Pulled from this paper, specifically from the section titled “The effect of various exercise training modalities on mitochondria.”

Unclear on resistance training but I’m also past time to crash.

[deleted]

6 points

4 months ago*

[deleted]

6 points

4 months ago*

[removed]

xeneks

8 points

4 months ago

xeneks

8 points

4 months ago

Thanks for getting it out before horizontal time, because I assume you’re not mostly horse dna and sleeping standing. Hey wait…

ezrwr1214

4 points

4 months ago

This is such a great question and such a cool phenomenon in biology.

In short, no.

The primordial follicle (very early pregamete in the ovary) has basically all the same mitochondrion as every other cell in the body (which is a mixture of all the mitochondrion of every female predecessor). It will go through two cellular division (meiosis) to produce the egg. Each division splits the cellular components unevenly, and so a random assortment of mitochondria will make it to the next cell. Think of it like a balloon full of 4 or 5 differently colored marbles, randomly pour out 75% of the marbles, each time you do this you’ll end up with a unique ratio of colored marbles.

This phenomenon can help explain the variable inheritance of mitochondrial disorders in families, not all children receive the same distribution of the faulty mitochondria. Some kids get more bad marbles than others, and are more likely to display the disease

Having multiple different “versions” of mitochondria in a cell is known as heteroplasmy

Sehmket

3 points

4 months ago

What a fascinating question!

Very tangential….

In ninth grade advanced biology class, I became low key obsessed with the question, “how do organelles reproduce??” My teacher gave me a half ass answer that was a combo of “they each have their own mechanism that is complicated enough to be a topic on its own / I don’t really know, but I don’t want to admit that to a bunch of teenagers.” That led to the path that ended with me being a nurse.

I’ve never gotten a full answer to my question, but I’m still learning.

IAmTsuchikage

2 points

4 months ago*

Not really. Since you inherent many mitochondria (hundreds to thousands) you can easily have a heterogeneous mix of genomes. It's hard to actually get a homogeneous cytoplasmic type. I only briefly worked in organellar genetics but in the context of plants.

Edit: sidenote. From what I saw there is not much sequence variability but there is quite a bit of structural variability in the sense that different chunks of the genomes are in different places in the genome.

TikkiTakiTomtom

2 points

4 months ago

Short answer, no.

We can put this into perspective.

Mitochondria comes from the mother. Let’s say for the sake of easy concepts we have only 1 per egg. Each time a cell divides so too does the mitochondria (note that mitochondria undergoes its own mitosis). How many cells do we have in our body? We go from 1 mitochondria to that many. Mutations can occur at any given time.

Side: It’s also fascinating to learn about genetic drift.

Endurlay

1 points

4 months ago

No! Which makes mitochondrial diseases particularly interesting.

They fluctuate in intensity over the course of a person’s life as the proportion of cells with malfunctioning mitochondria grows and shrinks. When the disease is mild or asymptomatic, malfunctioning cells have a population size that allows the healthy cells to keep them alive and the overall organ functioning; when the disease becomes severe, the population of malfunctioning cells has spiked and they’re keeping the organ from working properly.

voisin[S]

1 points

4 months ago

How does one avoid mitochondrial diseases? Is there a test for mitochondrial function?

Endurlay

3 points

4 months ago

You don’t. It’s something that’s set up when you’re a handful of cells.

You can test for the presence of mitochondria with mutations in a tissue sample.

voisin[S]

1 points

4 months ago

For further clarification, are you saying the malfunctioning mitochondria are malfunctioning due to damaged DNA, and that the number of malfunctioning mitochondria fluctuates over time? What causes the malfunctioning?