Yes, but I would think that if *both* parents have fertile 4, that chance should go from least 1 to 4 (or 1 to more than 4 if 4 were not the limit)
Just going on the premise that whether dominant or recessive trait, if both of your parents have a given trait the odds are high that the child will have that trait as well.
OR as Cece explained, we're supposed to be "breeding monsters together to increase their own abilities and thereby their value, or produce even stronger offspring."
And Katelyn explained, "The offspring is almost always more powerful and valuable than the parents, just through the power of science."
Now maybe Katelyn was giving a strong sell to make the MC feel better about his prospects, but until something in game says otherwise I'm going to assume that's how it's supposed to work.