Question

is there any science behind unicorns/ pegasis?

Answer 1

Pegasus, considering the fact that unicorns were, and still are, real. 

Answer 2

Yes, there is. This is because in advanced cases of DNA grafting, you would be able to graft wings onto a horse. This does not, however, account for the fact that the horse would not be able to use or take care of the wings that they were given.