Genes

Genes is a currency that represents "general knowledge of how the living creatures work". It's primarily used to craft plant seeds in the Greenhouse (or its upgrades), to breed weird animals like Psilamander, and also to craft bioengineered weapons/armor (e.g. Fungal Gun).

You can get genes from any plant seed at Sprouting Table (or its faster upgrade Xeno Research Lab, and even faster one Advanced Xenolab).

Strategy
Some plants yield significantly more seeds than others. Pick the plants that are fast-growing and yield many seeds, such as Algae, non-petal flowers like White Flower, etc. Vanilla perennial plants (such as Corn) yield very little seeds.

You can get more seeds by using a Growing Tray (or its upgrades) with a good fertilizer (preferably the fertilizer that not only decreases the seed use, but also increases yield).

Legacy information
In the old versions of Frackin' Universe, there were individual items like Chloroplast Boost or Aquatic Homeostasis. They are no longer used. If you still have any, you can convert them to Genes at Sprouting Table (or its upgrades).