Stunted plant or genetically impaired?

Yes, seeds are a bit like people, even though you have the same mother and father, each child is slightly genetically different. (excluding twins etc). Having said that, even twins are different, much like different phenotypes in the same strain of plants. When the breeders make seeds for you and I to buy, they possibly have dozens and dozens of mother plants, if not hundreds. Generally there are less father plants due to the vast amount of pollen produced by males. Even though the packet of seeds you got is meant to be OG Kush, theoretically, if you bought 10 seeds, each of those 10 seeds could have come from one of 10 different mother plants. So, to get one or two plants that are a little different to the rest of the packet is quite normal. This is what people refer to as "pheno hunting", looking for that one special outstanding individual plant that has something that no other plants have. The "Tiger Woods" plant. Think how many people play golf and how many Tiger Woods there are. That is what all breeders/growers are looking for, the "scholarship" plant. Your smaller OG plant is just being an individual that has chosen to be a little different to her sisters. She will still grow fine, and there is nothing that can really be done about it. She is special and will need a little extra time to get going. All will be well, but if she really concerns you, you could give it away or pull it out, but that wouldn't be fair to her. You never know, she might just have a "Tiger Woods" thing going on and produce flowers that are simply awesome. Give her a chance to get going. Hope this helps.... Organoman.

Sometimes not all seeds in the same package are as viable, vigorous, etc. It will likely keep chugging along as their special little sister, a little behind the rest. She will grow. I wouldn’t cull her unless its a space issue. Good luck, everything looks great