In science fiction there are thousands of scenarios which depict gene manipulation gone wrong. Its part of the "What IF" lure of the genre.
There are possible gene therapies that could promise a benefit to mankind.
Some are real science theory and others are a fantastic speculation.
For instance, Longevity...
Could humans live to 500 years old? Scientists believe genetic tweaks could significantly extend our lifespan
http://www.dailymail.co.uk/sciencetech/article-2523086/Could-humans-live-500-years-old-Scientists-believe-genetic-tweaks-significantly-extend-lifespan.html
The research raises the prospect of anti-ageing treatments based on genetic interactions, they said.
Why do we grow old?
http://isciencemag.co.uk/blog/why-do-we-grow-old/
Telomeres consist of the bases ‘TTAGGG’ repeated thousands of times at the ends of your chromosomes. These repeats then loop round like a lasso to create a ‘T-loop’ structure.
Telomeres, apart from being exceptionally fascinating, are hugely relevant to aging. In a sense, they are like the little plastic caps on the ends of your shoe laces. They are at the ends of your chromosomes to prevent the DNA (your shoe laces) from fraying; keeping your DNA intact.
When telomeres shorten in humans, they send a WARNING signal to the rest of the cell, and the cell begins to senesce: gene expression changes and the cell secretes factors that cause age-related diseases. Much like a candle slowly burning down until the flame goes out, our telomeres shorten as we age.
However, for some of our cells, the telomeres do not shorten. These cells are immortal. Our germ cells (those that produce eggs and sperm) and our stem cells are part of this small but significant immortal community. These cells contain a significant abundance of the enzyme telomerase, which is able to extend the telomere length by adding additional copies of the telomere repeat TTAGGG. Why can’t all of our cells have telomerase so we might have a chance of living forever?
How can telomeres help us? We now know that we expect telomere shortness to precede and predict the diseases of aging. Measuring telomere length may thus allow future generations to pre-empt, intercept and even prevent age-related diseases.
So basically, Gene therapy could increase your HEALTHY LIFESPAN.
Quite a substantial possible real life benefit.
Right now, our science is not able to successfully splice genes from different animals like we genetically splice plants and viruses. But consider what could happen if we could.
One of the most familiar animal hybrids is the mule, which is the product of a male donkey and a female horse. Another pair of celebrated hybrids are ligers (a male lion and a female tiger) and tigons (a female lion and a male tiger) which have characteristics of both species.
Source:
http://www.livescience.com/10659-hybrid-creatures-real-science-splice.html
Imagine a human that has the qualities of a fish.
Imagine a human modified to survive long periods of space travel.
While it may seem like pure fantasy right now, nano-technology and gene manipulation could bring such hybrids to futrition.
Consider that the Earth is constantly changing.
The conditions for life are also constantly changing.
There is less oxygen now than there was in the past.
Evolutionary gene manipulation isn't often able to keep up with those changes. Gene manipulation science may help us prevent or postpone evolutionary extinctions.
