The San Diego Zoo Institute for Conservation Research has the cell lines of 12 different northern white rhinos stored in freezing temperatures at its "Frozen Zoo."
Is that enough genetic diversity to rebuild the species?
Assuming I remember correctly. It takes only six individuals with the right breeding scheme to maintain a reasonable level of diversity. This is of course assuming that enough diversity is present in the founding population (ie the frozen samples).
There's something called the "50/500" rule, which broadly indicates that a population needs more than 50 effective members to avoid short-term extinction and more than 500 to avoid long-term inbreeding depression. You can read more about it, and the math that governs it, in this pdf: http://assets.press.princeton.edu/chapters/s12_9242.pdf
Genetic disorders are not the problem here. Things like disease are. Genetics can make it so one individual is more susceptible. Even if we can modify the genome at will, we have no information on how to modify the genome to make it do a certain thing. There's no room for error in this regard, as most mutations are going to be deleterious.
Moreover, CRISPR won't help individuals who are already affected by a genetic disorder. At most, perhaps it can help the progeny, but if the progeny isn't able to reproduce for another reason, then this point is also moot.
There is a limited subset of things for which gene therapies can work in adults. For example, thalassemia is caused by continued abnormal production of hemoglobin. If you fix the one defective gene, future hemoglobin will now be the correct variety. However, the old hemoglobin does not magically correct itself, and it will take time to clear. Meanwhile the damage it may have done to the liver and spleen will persist.
Gene therapy can also fix other conditions. For example, many complications of cystic fibrosis are caused by abnormal cilia not clearing mucus properly. You can switch the gene on to restore cilia function and clear the mucus. Sounds good so far, right?
Well, not quite. Cystic fibrosis can also cause men to be born without vas deferens -- the tubes that connect the testicles to the urethra and allow sperm to leave the penis. This happens because normal male development requires working cilia at the time the vas deferens is forming -- sometime in the first trimester of pregnancy. Once you pass this point, restoring normal cilia function will not make the organs that failed to form magically spring into being. That was a developmental event that does not happen again. There are no second chances for many stages of development. We have a long way to go before we can successfully treat genetic disease before the embryo starts to form.
I don't think these Rhinos are bacteria, so they may not be comparable.
For example:
Cheetahs are a threatened species. Low genetic diversity and resulting poor sperm quality has made breeding and survivorship difficult for cheetahs. Moreover, only about 5% of cheetahs survive to adulthood
That quote is a little misleading. Genetic evidence suggests that cheetahs went through two severe population bottlenecks around 100kya and 12kya, which is likely responsible for much of the low genetic diversity seen in the species today. Their threatened status is not the cause.
Does it matter how they lost genetic diversity? Whether the population bottleneck was caused by the end of the ice age 10K years ago, or by human poachers 10 years ago, this Rhino subspecies is down to 12 vials of eggs/sperm. And even 10,000 years later they are still struggling.
Are humans willing to foster this one Rhino population for 1000 years?
>> Genetic diversity is not a requirement for a species.
It is for any species on the edge of extinction. By definition, they are not adapting. Saddling them with the further burden of inbreeding isn't going to help.
Bacteria can also die in record numbers without much impact. If 1/2 of bacteria "children" die early due to genetic issues, little would change. But mammals invest much more energy into offspring than bacteria. Mortality rates matter.
Is that enough genetic diversity to rebuild the species?