Like the Chipmunks, the Chipettes were originally created for the musical medium, and later crossed over into cartoons. According to their creator, Janice Karman, she and Ross Bagdasarian, Jr., "...had been doing the albums at that point... We couldn't do the girl songs. I wanted to do female chipmunks that have counter personalities to the Chipmunks so we could do some girl tunes."
Bagdasarian also added in reference to the Chipettes characters, "It enables you to deal with issues that girls are going through that boys wouldn't necessarily be dealing with... We had a baby girl at the time. We wanted to let her know she can be president, or a soccer champion, or whatever... With the Chipettes we can handle those sorts of things."
It is worth noting, however, that the Chipettes of the cartoon series (Brittany, Jeanette and Eleanor) appeared on the small screen before appearing on any albums. Their first appearance on a Chipmunks album was on 1984's "Songs From Our TV Shows" which was released on March 4, 1984, nearly seven months after the Chipettes debuted on the first episode of the Alvin and the Chipmunks television series on September 17, 1983.
Although the Chipettes featured prominently on many Alvin and the Chipmunks albums, they received equal billing with the Chipmunks only on 1988's "Born to Rock."
There has been some speculation that the Chipettes may appear in a sequel to the popular Alvin and the Chipmunks film released in 2007. “There has been a lot of talk about it,” revealed Janice Karman, one of the film’s producers. “A lot of people have been asking about the little girls." Whether or not this comes to pass remains to be seen.
Although there is no proof of it in their decidedly American accents, the Chipettes were apparently born in Australia and orphaned at a very early age. Fortunately for them, their species seems to mature faster than human beings, and the Chipettes were able to walk, talk, and to some extent fend for themselves while they were still in their infancy, and no larger than the size of a human's hand.
Under unexplained circumstances, the sisters came to be living in the care of a young Australian girl by the name of Olivia. Olivia was herself an orphan, living in an institution run by a mean-spirited and exploitative woman called Ms. Grudge. Unfortunately for the young chipmunks, Grudge noticed their innate singing abilities and attempted to exploit them for her own benefit. Fleeing the orphanage, the Chipettes traveled to New York as stowaways on a freighter dubbed the "American Dreamer". For a time, the girls lived on the city streets, working at a variety of menial jobs, until Brittany saw an advertisement calling for singers to feature at a hotel in California. The sisters managed to scrape together bus fare and set out for Los Angeles, where they eventually landed the gig, taking on the professional name of "The Chipmunks".
During an engagement at another hotel, the girls encountered the original Chipmunks (Alvin, Simon, and Theodore) and their manager, David Seville. After a brief conflict over the Chipmunk name, Alvin dubbed the girls the "Chipettes".
The Chipmunks and the Chipettes became fast friends, and the Chipettes eventually settled in the Sevilles' suburban Los Angeles hometown and enrolled in the local school system. At this time, the girls lived on their own in an elaborate and well-furnished tree house. Unfortunately, school officials found out that the totally self-sufficient girls lived alone, and after a disastrous meeting in which Alvin and the Chipmunks posed as the parents of their friends, the girls were once again faced with the threat of life in an orphanage. In order to avoid this undesirable eventuality, the girls were adopted by Miss Beatrice Miller, the former leader of the World War II era dance troupe known as Miss Miller and the Thrillers, and a family friend of the Sevilles. It was at this time that they took on the surname of "Miller". Initially the girls felt frustrated with Miss Miller's old fashioned views and tastes (for example, she refused to let them go to school unless their skirts reached down to their ankles), but eventually bonded with her after they realized she shared their love of music.
Together, the Chipmunks and Chipettes shared a variety of adventures, perhaps the most exciting of which was their balloon race around the world. Over the years, each of the Chipettes engaged in on-again-off-again relationships with their Chipmunk counterparts--Simon with Jeanette, Theodore with Eleanor, and Alvin with Brittany. However, the relationship between Alvin and Brittany rarely went smoothly, as their similarly aggressive, egotistical personalities often clashed, in contrast to the more mellow interplay between Simon and Jeanette or Theodore and Eleanor. Alternatively, they were also shown to date human boys, just as the boys often showed an interest in human girls. It is notable that the Chipmunks and the Chipettes inhabit a relatively "realistic" world, in which theirs is the only sapient species aside from human beings, as opposed to a world full of anthropomorphized animals.
The Chipettes apparently lack the body fur of the Chipmunks, and also have more human-like hair on their heads, in what may be a case of sexual dimorphism in the species.