Shower Thought #66: The Immortal Cell

Everyone knows that a human's cell can only divide so many times before errors pile up and it dies. Do this enough times, and the human either gets cancer or gets enough internal damage for some other disease to off them.

But reproductive cells kinda don't?

(slightly NSFW talk, but in a clinical sense)

I'm going to focus on Eggs since sperm is a bit fragile and really only exist as DNA carriers.

So, take one egg cell. Compatible DNA gets injected in through some means, and it starts dividing. A clump of Stem Cells grows, then starts differentiating, and eventually you get one small human with a bunch of specialized cells that slowly start deteriorating over the course of a century. On the other hand, (assuming female) there is one clump of cells that instead specialize as Eggs. They divide a few times, then lay in wait for a few decades.

Assuming the Egg gets more DNA, it gets to restart the cycle again. Divide, specialize, produce another set of Eggs. And so on. Therefore, one could track one line of cells that, with a bit of DNA mixing, never really dies.

If you squint a little, this kinda looks like Time Lord regeneration. Just have the egg, like, never leave the body and instead just grow and replace from the inside.