Then There Were Three

The current population is 3: One female, one (effectively) gelding, one unknown gender and breeding condition. Previously there was a fourth male of potentially viable breeding condition.

Even if the had the best scenario for the (pre-loss) population size, 2 males and 2 females, and none of them have any close relation with each other, and they were kept as two 'breeding pairs,' with the offspring paired up so no turtle had to 'kiss his sister,' the next generation down would all be first cousins to each other at most.

The population is WELL below a sustainable size, and with the current situation, one breedable female, and one potential 'breedable male,' (The gelding has metaphorically climbed out of the gene pool and is toweling off in the locker room for his nature walk into oblivion.) even if the numbers could be brought up, there is no genetic diversity, harmful regressive traits will be expressed in record numbers in the grandchildren of this ultimate 'population bottleneck.'

We are watching yet another species head off into the land of the "Used-to-be," and all we still could have learned from studying it will be Lost Forever.

Unfortunately you're probably right. There are species that survived the brink of extinction but are bottle necked now in the gene pool. One species was a type of kiwi in New Zealand. I think they only had 5 kiwi left and successfully brought the species back but has bottle necking in the gene pool. So it's possible.

Yeah, and the only way to get out of the bottlenecking is with generations and mutations, something that Nature may not give a species enough time to do.

Other times it gets so bad, a species ends up absolutely clonal: it has no 'dominant' or 'recessive' genes anymore, it's chromasomes are complete copies of each other all the way down. Bananas are like this now, every banana in the supermarket is a genetic carbon copy of every other banana in all the stores. That's also why 'banana flavoring' does not taste like banana to us; that flavoring was designed to match the Gross Michel, the 'Big Mike' cultivar, that was nearly wiped out by the Panama disease. Since all Big Mikes were clones of all other Big Mikes, the fungus that was fatal to one was fatal to all, and the entire species was devastated, aside from a small section in Asia, where the fungus has apearantly never visited. Since most of the world is now lethal to the Big Mike plants, we make due with the smaller, less flavorful Cavendash.

...At least, until the next 'Panama disease' comes around to attack this 'clone family.'

The worst part is that we cannot undue the damage we have done to the banana; it no longer produces viable seeds, all 'new' banana plants are effectively 'clippings' from their clone mother/sister. We could try starting again with the 'wild-type' banana plant, but that species is full of large, hard seeds; 'domesticating' it into something people would want to eat would just send it down the same road to clonal stagnation as we've done to all the other domesticated varieties.

I hear that there's a new type of panama disease that's starting to wipe out the Cavendash bananas and that once it reaches Brazil, you can kiss them good-bye.

Yup, but it's not a 'new type,' it's the same fungus that ate Big Mike, this is just a new strain, one with a taste for Canendash. It was bound to happen; evolution, survival of the fittest, if a species loses its primary food source, it will either perish, or it will adapt to a new food. From what I've heard, the Cavendash-eating variety of the fungus can't hurt Big Mike, but the Big-Mike eating variety is still in the soil there, not a lot, it's barely surviving on whatever it's eating now. but you plant a Big Mike, or a 'painstakingly hand-polinated' big mike/cavendash hybrid⁽¹⁾ and the Big Mike eating fungus will thrive on the newly planted 'feast.'

Notes:

1. They're working on those, appearantly, but either the hybridation does not 'take,' or they get bananas with big, hard seeds,and those seeds produce seedless bananas without the Big Mike gene sets they're looking for to fight off the fungus.
   

My bad, when I said a new type, I meant a new strain of the fungus. I agree, evolution has a way of either fixing old problems or getting rid of them by survival of the fittest, i.e. extinction. Today's modern bananas will soon be a thing of the past, just a matter of time. Just like that Yangtze softshell tortoise.