if a gecko has high yellow, it shows. it does not carry the genes if it is not present on that animal. high yellow is line bred, meaning that if you have one gecko, a normal leo, and breed it to a really high yellow leo you will get a high yellow baby. it is a "compromise" of the two. this type of trait is referred to as line bred because line (meaning lineage) is how the morphs get more defined. if those two geckos have babies you might take the baby with the highest yellow and breed it back to the "nicer" parent, usually the dad. if you are doing this you also want to incubate the eggs at a lower temp. so you get more females. the male should always be the nicer of the breeding geckos as he will get always get his genes into the next generation, and the female, if you are keeping more than one of them, will not. i hope this helps.