In Known Space a certain amount of genetic tinkering is regarded as perfectly acceptable and normal, but there are still people out there who regard it as 'unnatural', and researchers and technologists do sometimes go to far.
On many worlds there are developed ecosystems, and most of these are based on local variations on proteins, nucleic acids, carbohydrates and fats. These are not always close enough to Earth's native biochemistry to be easily digested, so genetic engineers put synthetic enzymes into normal gut bacteria to help things along. Eat a yoghurt with the bacterial mix and over a few days (not usually accompanied by diarrhoea, vomiting and stomach cramps) your gut flora will adapt to local food.
Starship crews who skip from planet to planet frequently hate this and try and stick to imported food, but medical officers will passenger vessels will administer the bugs while aboard ship.
For any planet where this is action roll 4+ vs Endurance plus skill of medical officer supervising. A failed roll will result in 1d6 days of illness reducing END and STR by 2 and all skill rolls by 1.
From TL9 onwards it becomes possible to take stem cells from a sick person and grow quite complex organs in the lab. This makes transplants of most of the viscera and even replacement bone and muscles far easier. The 5000Cr cost to replace lost characteristics due to injury are reflected by this and this can be used to replace those lost by ageing as well, but only 1 point per characteristic.
At TL 10 one rather stupid but popular implant are specially crafted steroid glands. They will increase STR by 2, but the cost is advanced ageing, with ageing rolls made each 3 years rather then each 4.
At TL 11 'improvements' become possible. Livers that can synthesise Vitamin C and essential amino acids are a comparative doddle, hard wearing kidneys less prone to kidney stones, lungs with better self cleaning capacity etc. For 15,000 Cr (give or take), a PC can improve END by 1.
Also at TL 12 it becomes possible to put in improved muscle fibres and strengthened bones, giving +1 STR for 20,000 Cr, to a max of 3 STR as various parts of the body are improved. The appearance of these at higher levels can be quite ungainly, for each point gained over 12, one point of DEX is lost.
At TL9 knowledge of the functions of the thousands of genes means that embryo selection is possible. A batch of egg cells are fertilised artificially and DNA analysis is used to select the 'best' by the lights of the parents. At TL 7 and 8 this is used to eliminate embryos with inherited genetic disease, but at TL 9 'positive' features can be selected, though the influence of genes is not absolute. If a person has SS 9+ and TL 9+ they can swap 1d3 stat points between STR, END, DEX and INT. At higher TL it becomes cheaper and easier, SS 8+ at TL 10, SS 7+ at TL 11+.
Germline modification means any changes made to the genes is passed on to the next generation, creating the risk of a 'genetic aristocracy'. Different cultures take different views on this, mostly negative, but fortunately it isn't that easy to do. Even at TL 12 implanted genes are slightly unstable, and the genes either have no effect, or even cause disabilities.
The wild and wacky stuff
Secret projects to radically modify human beings have taken place, but they have always thrown up many failures. Rumours that this or that corporation or dictator has financed such a secret project float about regularly. Nothing has been proved however.
- A PC discovers that he has been subject to peculiar experiment – he has Einstein's brain. The DNA from Einstein was stripped of its immunological markers, the PCs own substituted and, as an embryo, the stem cells that lead to the brain substituted. Who did this? Has it made any practical difference? Did it even work?
- In a care home for people with learning disabilities a doctor has made a troubling discovery – scraps of DNA that look like tags from a gene implant. The person they come from has a shadowy history, being abandoned in a hospital as a child, and severe autism means they are not at all communicative about what happened. Where did this person come from?
- A clinic is offering a rather silly modification – pointy and other modified ears at knock down price. They have become all the rage among the fashionistas. Thing is it's being run by Plesios PLC, and unsavoury rumours link them to a neo-fascist regime. What else are they putting into their patients while the ears are being sewn on?
- Some twit has implanted roid glands into Alsatian dogs, and with a cybernetic jaw, IR vision eyes and natty bullet proof dog coat you have a fantastic guard dog. Just introduced as starport security, and already marmalised half a dozen thieves out by the warehouses. You have packs of cyber implanted, steroid crazed bullet proof hounds between you and your starship and there's no sign of the handlers.
- The Metelli family are very wealthy, have produced great scientists, a number of eccentric artists and have a politician or two in the family. Gerald Metelli is in the running for president of the colony of New Campagna, his rivals want definitive proof that they have been using germline genetics and do bit of rabble rousing. Get DNA from one of the clan and don't get caught.