Hi I think I experienced a bug but I am not sure. I bread Shana who is a level 50 with one green star, with an animal with 2 green stars. I thought that the result had to be an animal with 2 green stars but the offspring only had one? is this a bug or my misunderstanding?

If the second pet with 2 stars was not lvl 50 then this is not a bug.

The rules of acquiring Genetic Power:

1. If both of the parents have level 50, their child will get +1 Genetic Power.
   If one of the parents is level 50 and the other is not, the child will get +1 Genetic Power if it has 7 or more dominant genes from the level 50 parent.
2. If both of the parents has similar grade of Genetic Power, the child will get this grade and +1 grade if one or both parents have maximum level (according to the first rule).
3. If parents have a difference of 1 grade of Genetic Power, the child will get the higher grade if it has inherited 7 or more dominant genes from the parent with higher grade. Genetic Power through level can be only acquired but not inherited in this case, thus the levels of parents do not play any role here and do not affect the Genetic Power grade of the child until they are both Lvl 50.
4. If parents has a difference of 2 or more grades of Genetic Power, the child won't get Genetic Power grade for parents' genes, it can get only 1 Grade for parents' levels.
5. Breeding a level 50 pet with no Genetic Power and level < 50 pet with Genetic Power Grade 1 will always result in a baby with Genetic Power Grade 1.

thank you so basicaly 

level 50 with 1 genetic power + leval 17 with 2 genetic power can = baby 1 genetic power, because even though father is got a genetic power of 2 he is not leval 50

Yep, level only plays a factor in GP  when both parents are lvl 50. If the baby had 7 or more dominant genes from the father the baby would have gotten his GP2, but that must not have been the case. I believe the chances of that happening is something like 1:5. That isn't an official number so it may be wrong, but it's what I got from my observations a while back when breeding.