system
Given the following post, respond as if you're commenting on Reddit:
human
GMOs- engineered genes in crops don't spread into the wild, into other species, do they?
gpt
If the engineered plant or animal can interbreed with a native (or natively-cultivated) plant or animal, the engineered variants can be passed to offspring, just like any other gene. A genetically modified organism is just like the non-engineered organism plus a tiny bit of DNA added or changed in order to add, augment or change some function - they aren't fantastical beasts with lions and eagles spliced together. GMO corn is still corn, GMO soybeans are still soybeans and GMO salmon is still salmon.

If no native species exists that the engineered plant/animal can breed with to produce viable offspring, or the engineered plant/animal is rendered infertile or otherwise isolated, no transfer into the environment will occur. 

As far as whether they'll take over wreak havoc on the local flora and fauna - that depends strongly on exactly what was engineered (genetic engineering is only a technique) and if there were any impacts on organismal fitness - not all modifications are made with evolutionary fitness in mind, and some variants may be less "competitive" against their wild relatives.