A phenotype is a particular trait or characteristic of a plant. It could be high yield, short growing mature or fruity aroma. A seed bank will normally give you a description of a strain, listing the best phenotype. F2 stock phenotypes will vary more than F1 stock, and as you progress to F3, F4 etc, the variation becomes greater.
So basically, when you order an F2 stock of seed, be prepared for some variation in the plants phenotype. However no potency or yield is lost between F1 and F2 plants.
When ordering F2 stock, the idea is to search out the better phenotypes, and clone them so in future you only work with the best genetics of the bunch. With F1 stock, you should have more uniform plants that all perform similar, and if the breeders done his job correctly, this should be as close to the original description that tempted you to buy the seeds in the first place as you can get!
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