I've seen what comes of breeding a mousie that's half English to a mousie bred by me; he was Monster, a foot long hunk of black buckness. This can't be due to that, as I've had no English show genes input in the last four years. The last one was Hazel, one of the mosuies sent to me from RodentFest four years ago. (The albinos I got off the truck must have a touch of English show mouse in them too. I'm not sure if I'm going to use and of them to mix with my current lines, as there seems to be a lack of good health, as two of them are already gone.) She was a long haired satin recessive yellow doe, very long and lovely, and I didn't know at the time I started breeding her that she was hiding her tri genes. So the potential for size is in there...I like to think I've done well selecting individuals for breeding that improve the size and type of my meeces. But I don't always choose for those things, as I'm primarily interested in color and markings. Given the choice of individuals mousies that both have good qualities, I will choose the bigger to breed.
I wonder how much, if any, English blood there is in the huge white mousies I bred off of my reptile store boy, Berg. I know PEW's tend to be bigger to start with, and I am planning on continuing with that line just for giggles to find out how long it takes to see improvement in the typiness of that sort of mousie.
In any case, this little sizzler, being a light color, is prone to obesity anyway, and I hope it isn't too fat when it's time to breed.