The Sweetgrass derived from that crossing may be slightly smaller than Sweetgrass that have not gone through that crossing which is due to the different body characteristics of the two varieties but it is definitely not an average since Royal Palms are significantly smaller than Sweetgrass.This is the part has me confused! The Royal Palm/Sweetgrass cross will presumably be the average of the parents in terms of size and shape, but it's still considered Sweetgrass?! Does that mean Sweetgrass is just a color, with no consideration for size or shape?
The Narragansett color gene (nn or n-) is the only difference in the color genetics between the Royal Palm and the Sweetgrass.
There is a difference in the other body conformation and make up genes that appears that the ones that the Sweetgrass has may be dominant to the ones that the Royal Palm has. I have not seen any DNA studies of the genes controlling the body shape for turkeys.
We do know that there is a gene or genes controlling the broad breast aspect.