Let me explain this with pics cuz we all love great representations and feel this is great knowledge to continue to share so here goes…
A photoperiod is gonna be AA and autoflower is aa, anytime u see Aa that means a faster finishing photoperiod since the photo trait is always dominant and auto being recessive
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So first cross with a full auto would give you all fast finishing photos, cross any of those fast finishing photos together and you get…
This gives you 25%photo, 25%auto and 50% fast finish
Find the 25%autos and cross em and you have an isolated auto gene
Now if u took that isolated autoflower and cross it with a fast finish photo that would give you the half and half photo and auto
Same goes for the other way to though if u cross a fast finish photo with a true photo ur gonna get half and half of fast finish photo and photo
This is great info because you can in fact take a good photo and auto cross em together and take either direction with em following these charts if you want the final work to be auto or photo, my concern is if seed banks are unleashing fast finishing seeds carrying the gene and people end up with autos trying to do random breeding