Think about that—if mothers didn’t pass mitochondria to sons, and fathers don’t pass mitochondria to anyone, then males would not have mitochondria.
(Hint-males have mitochondria.)
Also, mitochondria are not found in the cellular nucleus, and the number of eukaryotic organisms currently known to have no mitochordria is one.
Both are consistent with my understanding and what I have been saying too.
To be blunt, your understanding—isn’t.
“Next” as in her grandchildren’s generation.
Her son(s) have her mDNA. They however will not pass it on to their children (as you note, the sperm has no mDNA and the next generation of sons and daughters will get their mDNA from their mother.)
Hence mDNA traces mother to daughter to … however many greats granddaughter in unbroken female line. Males are mDNA dead ends. And Y DNA is only passed father to son and on.
But neither the Y chromosome or the mitochondria are organisms.
Well, mostly.
Yes, it is now indisputably part of the cell, an organelle. The existence of mitochondrial DNA and its pattern of inheritance does not imply that a mitochondrion is still an independent organism. Mycoplasma genitalium has 525 genes, the fewest of any known organism. Human mitochondria have 37. If something has no possible independent existence, there is no sensible way that you can consider it to be a separate organism.
I think you have misconstrued explanations of the endosymbiotic theory that the evolutionary origin of mitochondria in the long distant past was the engulfment of independent organisms. It took a long time for the endosymbiotic theory to be proposed and even longer for it to be widely accepted (and not universally so even now). That would not have been the case if they were still independent organisms living inside other cells.
Most of the original endosymbiont’s DNA is now part of the nuclear genome. Another very large chunk of your genome came from ancient viruses. These origins do not imply that a cell still contains multiple separate entities, any more than the fact that half of your nuclear DNA came from your mother and half from your father implies implies the existence of two separate entities.
Interesting that there are some species that break the general pattern and that there is some sense about whether or not a few mitochondria from dads might slip in as the sperm is not absolutely devoid of mitochondria after all.
But for general understanding purposes @am77494’s understanding about a female with only sons being a dead end for her mtDNA was pretty much right and should be recognized as such.
It WOULD be interesting to have mitochondria that could transmit like viruses…
I read that as saying females do not pass on mitochondria to their own sons.
Hence the need to clarify what “next generation” means for the statement to be accurate.
The Y chromosome has a similar unusual pattern of inheritance, being passed solely down the male line.
And it’s also worth nothing that any allele in your nuclear genome can “go extinct” while the rest of the genome keeps going. If you have one child, half of your DNA is not inhertied by anyone, and if that contains any unique allele, that allele “goes extinct” when you die.
So none of these patterns of inheritance are determinants of whether something should be considered a separate organism.
Spermatozoa contain 50-75 mitochondria.
As noted by @Darren_Garrison previously. (Seriously people, and also looking at you @Riemann, you may want to consider reading others’ contributions…)
And again for purposes up through undergraduate and even medical school biology, and certainly for the questions of the OP, the fact is that sperm have virtually no mitochondria, with exception of a few species, such as bivalve mollusks, paternal contribution to offspring mtDNA can be approximated as zero.
I had professors like this. So interested in the rare exceptions and graduate level arcana that they could not explain the basics worth shit.
Yet is is fertilized – I guess that’s the term – by a sperm cell, one of the smallest human cells there are. I understand the logistical reasons for this factoid but find it amusing nevertheless.
Spermatazoa have plenty of mitochondria for their size and structure (which is almost entirely nucleus and flagellum). Spermatazoa have an intense need for mitochondia because they need to burn lots of energy. They are like a spacecraft with fuel tanks strapped to the outside wherever they will fit. It is that they are mistly unused in the fertilized egg. (Feel free to dismiss that as an unimportant graduate-level detail if you wish.)
Squid have giant axons that actually are naked-eye visible. I always found astonishing there were single cells large enough to be plainly visible
Yes it is that they are in most species nearly always completely unused. And that its 50 to 75 mitochondria, whatever their fate, are entering an ovum which, in the human case, has 100,000 to 600,000 mitochondria. (Liver cells have only a thousand or so.)
I guess we’re not supposed to contribute here. @DSeid has spoken.
Moderator Note
Saying that everyone here can’t explain the basics worth shit is an insult directed at other users. If something isn’t explained worth shit, just correct the explanation. Don’t go on an all out attack on everyone in the thread.
If you want to be snarky and have a go at another user, you know where the Pit is. This is FQ, not the Pit. Post accordingly.
I apologize for the allusion to my professors who were so caught up in advanced stuff that they were shit at teaching the basics, if such offended. Its intent was not to insult, more a story about the problems of not addressing the room, albeit I can see how it may have been read as such.
And I stand by the point. Comments like “your understanding—isn’t.” when the understanding as expressed is pretty much on target for a generally well educated person, should be corrected.
For general understanding purposes sperm can be thought of as not having any significant to no mitochondrial contribution to future generations, as the standard understanding, other than for a few species.
As to question regarding mitochondria as individual organisms … with other cells as their niche in an obligate symbiotic relationship … we don’t consider as such but I am not sure that @Riemann’s explanation of why quite suffices.
There are obligate symbiotic relationships in which both are considered organisms in their own right but have co-evolved to the point that neither could survive without the other. Lichen as the obvious case.
Viruses and their dependence on host cells to reproduce at least have a debate regarding their status as living.