How transgenic could a transgenic mouse be and remain a mouse?

[Hoosier Daddy]

I work with transgenic mice, and I was musing--idly--on a question of just how much of a mouse needs to remain a mouse for that mouse as a whole to likewise remain a mouse? Of course, this is a purely theoretical question, given the number of genes in a mouse genome.

Likewise, if the only parts of the transgene are the coding sequences but not the concomitant promoters and terminators, how do they count or not toward this question?
There seems to be some really sad and sorry ignorance out there. There is NO BLANK GENETIC MATERIAL! I was referring to promoters and terminators in addition to coding sequence. I want to go EXTERMINATE the idiot "teachers" who have kept telling the unwashed masses that only the coding sequences are "real" genetic material and the rest is "junk DNA". That idea died DECADES ago among scientists.