I went to breed one of my creatures and their gene strength jumped from +1M to +2.5M in one breed.
Some formula broke around +4B to +9B gene strength.
See INT stat.
also, the time to calculate gene strength for eggs goes up after about +20M gene strength.
At +3B to 9B it took 30 minutes or more to go from confirming the breed to showing the creatures merging and producing an egg.