http://www.gameinformer.com/b/news/archive/2015/01/09/mass-effect-39-s-commander-shepard-original-conceived-of-as-a-woman.aspx
When BioWare first revealed the Mass Effect trilogy, the company showed off gameplay that featured a male Shepard, but the character's earliest incarnation was as a female.
Nearly 20 percent of Mass Effect players played through the game with a female Commander Shepard, but I wonder if that number would have been higher if BioWare had initially advertised the game with a female Shepard in the lead role. According to Mass Effect 1 and 2 lead animator Jonathan Cooper's twitter feed, BioWare always intended to let players pick their Shepard's gender, but the game's earliest animation tests reveal a female Shepard.
The videos are in the link