I'm sorry, but I'm not 100% clear on what your question is. Are you asking whether it would be a valid sciene fair project, to compare the DNA of different animals? If so, I would say that, while you should check the rules of your individual fair, DNA tests are generally allowed. Often you have to submit an extra form for scientific review, but this shouldn't be a problem, as you are not doing anything dangerous or unethical.
This sounds like a very interesting line of thinking to persue! The DNA projects I have seen a science fairs have tended to do very well, so, if your daughter is intereted in DNA, she should by all means go for it!
As for specific ideas, those are among the hardest part of any science fair project, if your daughter wants to do well. The Science Buddies Idea Generator has a lot of good project ideas, but, if your daughter is at a really high level of science fair competition, I would have to suggest trying to find something that has not been widely explored in the past. The fountain of youth idea, if I am understanding it correctly, is an intruiging starting point, although I could imagine that it could potentially be very difficult. You could compare DNA within a given species, such as turtles, which might be interesting, although you would have to determine why this would be a better way to investigate the question than comparing human DNA. You could also try comparing DNA across species, some of which are more long-lived than others, but the issue is that different species' lifespans are often not directly genetic. There is a lot of research to suggest that, while smaller animals tend to have shorter lives, all of their internal rythyms are sped up to the point where they tend to have the same amount of life experience as larger, slower animals. In fact, some studies have found a direct correlation between metabolism and life-span. ( http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&uid=15855403&cmd=showdetailview&indexed=google
). While this could suggest that lifespan across different species may be too complicated to anylyze purely through DNA, it is important to note that DNA also controls metabolism, so this may still be a viable idea. This is discussed more thouroughly here: http://www.mccmedia.com/pipermail/brin-l/Week-of-Mon-20040607/019939.html
. The mitochondrial DNA discussed in the second section may be of particular interest to your daughter.
If your daughter does decide to persue a project along these lines, I would strongly reccomend finding her a very knowledgable and experienced mentor, as DNA analysis is rapidly developing and probably not yet at the point where it is easy to self-teach. A mentor may also have some better topic suggestions.
I hope this answered some of your questions, and provided some sort of jumping off point into a very interesting but complex field. If you have any further questions feel free to ask. Good luck!
- Emily Dolson