system
Given the following post, respond as if you're commenting on Reddit:
human
[TMNT] What would the offspring be like if the turtles fertilized some non-intelligent females of their same species?
gpt
In nature a new species can be created when an existing species is divided somehow and the two groups begin to evolve differently. Over time mutations will arise in both populations and once sufficient differences have occurred it will no longer be possible for the two groups to mate and create viable children. 

Although that's not exactly what happened here, certainly the four turtles underwent extreme mutations and it seems highly unlikely that they would still be able to produce viable offspring with females of their previous species. 

I think that if they mated then the offspring would not be viable enough to come to term and the eggs would abort in early development. It's shame but the four turtles will likely be the first and last of their species and once they are dead their bodies will be stuffed and put on display in the natural history museum. Well that's what I'd do with them anyway.