[annie123 (OP)]

If a woman only has male descendants in the next two generations does her mitochondria become extinct?If not how does it get passed down?

[evan_au]

If a woman X has a sister, or her mother's sister, their children will have the same mitochondria as woman X.
Thus the mitochondrial DNA of woman X may be passed down through her female relatives.

Bear in mind that a human egg cell has over 100,000 mitochondria, so the exact mix of mitochondria will change from generation to generation. High rates of random mutations in mitochondrial DNA than nuclear DNA will result in genetic changes to the mitochondrial DNA passed from mother to daughter.
See: https://en.wikipedia.org/wiki/Mitochondrial_DNA#Mitochondrial_inheritance

Not every part of everyone's DNA will be passed on to the next generation; even if you have 2 children, on average you will only pass on 75% of your nuclear DNA to the next generation.

[annie123 (OP)]

So, since I don't have sisters, and my mother's sisters didn't reproduce, and I only have sons who have sons am I to understand that whatever of me is physically present on this planet will not continue further? In other words, my only chance of a specious immortality is negated by biology?

[hamdani yusuf]

So, since I don't have sisters, and my mother's sisters didn't reproduce, and I only have sons who have sons am I to understand that whatever of me is physically present on this planet will not continue further? In other words, my only chance of a specious immortality is negated by biology?

You can donate your mitochondria, like in this case :
https://www.newscientist.com/article/2107219-exclusive-worlds-first-baby-born-with-new-3-parent-technique/

[evan_au]

I only have sons who have sons am I to understand that whatever of me is physically present on this planet will not continue further? In other words, my only chance of a specious immortality is negated by biology?

The fact that you have children and grandchildren means that part of your genes will continue into the future (but nobody can be confident for how long).
- A sample of your nuclear DNA (3 billion base pairs) has been passed on to the next generation, even if mitochondrial DNA (17 thousand base pairs) has not; 99.9994% participation is pretty successful!
- Hopefully, your experience, wisdom, guidance, training and nurturing have also been passed on to these generations.
- And to the friends of your children, and their families
- Hopefully, you have also had an opportunity to contribute to your extended family, your friends, your community, workplace, the public, and perhaps the country.
- In a wider sense, your contributions to the Naked Scientists forum have benefitted people around the world
- So its a bit unfair to say that you have missed your opportunity for immortality
https://en.wikipedia.org/wiki/Human_genome#Molecular_organization_and_gene_content

Reading between the lines, you might have some brothers who had children?
- They will share much of your nuclear DNA
- Even if you had no children, much of your DNA would be passed on through nieces and nephews.

Even if you were the last of the Romanovs, you share 99.9% of your DNA with other members of the human race, so much of your DNA would be passed on through them - unless/until the human race goes extinct
- The average lifetime of a mammal species is around 1 million years; some pundits forsee a number of challenges just in the next century
- if the human race evolves into something extra-terrestrial and/or post-human, then some of our shared genetic legacy will be passed on through them

But at some level, mortality does seem unfair - I guess that is why Christians celebrate Easter...

[annie123 (OP)]

"You can donate your mitochondria, like in this case :
https://www.newscientist.com/article/2107219-exclusive-worlds-first-baby-born-with-new-3-parent-technique/"

yes i read about this but I was mainly interested in my own family line.

To evan-au

I thought i had learned somewhere that it was the female transfer of mitochondria that was the key to the continuation of a line and that it was the critical agent in reproduction of a mammal's essential characteristics. Anyway, your points are taken. I was just curious - I don't have any apocalyptic despair about not becoming immortal per se -= "I am a part of all that ever is And all that ever was" as one poet I admire has written. And yes my brother has daughters so something of me will go on in the specifically mammalian context I suppose. Looking back at my ancestors I don't find that the non physical characteristics of a person carry on much more than a couple of generations unless they were distinguished people but that's another question more difficult to analyse.
 Thanks.

[evan_au]

I thought i had learned somewhere that it was the female transfer of mitochondria that was the key to the continuation of a line

There are many ways to define a genetic line, and mitochondria are not the only way to define it.
- Mitochondria are often used to identify a maternal line
- The Y Chromosome is often used to define a paternal line
- The other chromosomes also form a genetic line, but have a more complex pattern of inheritance; for example, the pattern of hemophilia in the royal families of Europe.
See: https://en.wikipedia.org/wiki/Haemophilia_in_European_royalty

As an example, some researchers estimated that about 16 million men alive today share a Y chromosome with Genghis Khan (and his father and grandfather) - mostly concentrated in Mongolia, China, India, Russia and the Middle East (areas conquered by the Mongol Empire).
See: https://en.wikipedia.org/wiki/Descent_from_Genghis_Khan#DNA_evidence