I know I might be generalizing but to me it seens heavy music is fairly male dominated. Most heavy metal bands are composed of only men, and having a female member in one is so unusual it draws attention. Commonly, I see women in bands that have a more melodic style, such as Nightwish. There are bands like Exile, Sceptic, there was also Cadaveria who left her band and went solo and the singer from Cripper, but none of them are the in the lead guitar, rarely on bass. Also, the metal bands who were responsible for the foundation of what is metal music, all had only male members. Black Sabbath, ACDC, Metallica, Slayer, Anthrax, Exodus, Rainbow, Iron Maiden, Megadeth, Deep Purple, Venom, Kiss, everyone from late 70's and the 80's, the whole New Wave of British Heavy Metal, the trash bands from the US, had men everywhere.
There are women in the scene, but somehow their numbers seem very small. I see plenty of women playing piano, acoustic guitar and being amazing at it. I suppose heavy music is by nature aggressive, and perhaps women don't identify well with it for that reason. But even so, the bass and the eletric guitar instruments seen to be lacking in representatives among women, as none of the virtuosos I know from those instruments are women. Steve Vai, Joe Satriani, Eric Clapton, they are all guys.
I can't understand why this is so. The music scene seens to be fairly open regarding gender roles, at least to me, and nothing stops a girl from picking up a guitar and learning Vai's solos. Myself, I play the bass and the guitar, and I have always been the only female in the bands I have been in. even those who weren't playing heavy music, just common rock stuff.