Gaz is the daughter of Professor Membrane, as well as his youngest child. It has been said, however, that Gaz and Dib were created by the Professor in his lab, and are therefore not his biological children. Nevertheless, Membrane still treats them as such... when he's around. Usually, the Professor is busy in his lab, and communicates with his children via recorded messages.
However, based on their live interactions, it is clear that the Professor and Gaz have a lot in common: Both of them have little patience for Dib's antics, for their own reasons (the Professor considers Dib insane, while Gaz just thinks he's annoying).
Professor Membrane often neglects both of his children, maintaining contact with them mostly through floating screens that are oftentimes pre-recorded. However, he shows affection towards them in limited occasions; in Gaz, Taster of Pork, when the Professor can't invent a cure for her daughter's "disease", he becomes rather desperate. He "protects" Gaz by putting her in a special insulating suit and confining her to quarantine, then he builds an entire speciality area to try to find the cure. In Game Slave 2, he insists in her being escorted by Dib to the midnight Game Slave 2 video game console sale, because it could be too "dangerous" to go by herself, showing actual worry. However, he does show willingness to let his very young children wander the streets at night, which leaves up to debate how much he really cares about their safety. It can be argued that Gaz is Professor Membrane's favorite of the two, considering that her brother often makes a fool of himself with his paranormal preoccupation. He even goes so far as to state that Gaz should find Dib and "Make sure he doesn't do anything embarrassing." He shows a tendency of picking her up a lot, often to carry her on his shoulder. He has stated on occasion that "You're my funny child!" Compared to Dib, who would likely be his "insane child."
Professor Membrane might be the only person to which Gaz shows a level of respect and love to. The biggest example of this is Bloaty's Pizza Hog, showing that the "Family Dinner Night" (the only night in the year in which Gaz, Dib and Professor Membrane pass time together as a family) is important enough for her to go to save Dib, and bring him in time and unharmed. It should be noticed that in Bloaty's Pizza Hog she doesn't care for Dib fighting with Zim in the night of the event, and tries to convince Professor Membrane to exclude Dib from the event, but when Professor Membrane refuses to go without Dib, it is then that she goes to save him. She seems to be the only one of them that cares that they rarely get to see their father, and is therefore more willing to go out of her way to spend time with him when she can. Although she seems to admire her father, she seems to get extremely angered at him for lying to her in Dibship Rising, perhaps the only seen time she ever does get angry at him.