Santa's Little Helper the dog was a "sympathetic" character. Welker has been praised by staff members for his performances on the show. David Mirkin has noted that "he can do anything, and it fits perfectly. You forget you're listening to a guy, and he's a pleasure to work with." Groening has commented that he was "unbelievably good" at doing animal noises. After 1995, Castellaneta voiced Santa's Little Helper on his own while Welker performed other animal noises until his full departure in 2002, when he was denied a pay raise. In the "questions and answers" section on his website, Welker revealed that the
Helper dependent virus and capsid encoding DNA, plus helper DNA. Every cell that is successfully transfected with all three DNA fragments will produce the necessary proteins to produce infective viruses. These viruses will only have transgenic DNA encapsidated and therefore once they've infected a patient's cell, they will not be capable of reproducing. Helper dependent viruses can also occur in nature without being "gutted". The term satellite virus has been given to a large group of viruses that all require the presence of another virus to replicate. Many of these are plant viruses, but animal viruses can be seen in the case of