I think the thing you're getting at with your question can be answered by thinking about how different various types of geckos are fro each other based on biological classification. The biological classification system starts with the biggest divisions (i.e. "Kingdom" or plant vs. animal) and continues like a branching tree through Phylum, Class, Order, Family, Genus, and Species.
Leopard geckos are its own species. Their genus is Eublepharis which includes all other geckos with eyelids Your day geckos don't have eyelids, so they are in a different genus and they relate to the leopard gecko through the next level up, the "Family", which in this case is Gekkonidae (or "gecko"). Once a type of gecko diverges in its classification from another gecko at the Family level, the two gecko types are going to be quite different. In this case, as mentioned above, one type is awake mostly right before and after sunset/rise while the other is active during the day, and one type stores fat in its tail while the other type doesn't. Make sense?
Aliza
Leopard geckos are its own species. Their genus is Eublepharis which includes all other geckos with eyelids Your day geckos don't have eyelids, so they are in a different genus and they relate to the leopard gecko through the next level up, the "Family", which in this case is Gekkonidae (or "gecko"). Once a type of gecko diverges in its classification from another gecko at the Family level, the two gecko types are going to be quite different. In this case, as mentioned above, one type is awake mostly right before and after sunset/rise while the other is active during the day, and one type stores fat in its tail while the other type doesn't. Make sense?
Aliza