Because of the Major Focus male (or female) I'm now wondering if the lab to i.e. develop a healing spell is using the major focus if the spell that could heal both gender or only if the magus would have restrict the spell to one gender to get the bonus?
I'd definitely say restricted.
If you keep the spell restricted to males or females, then the Focus always applies, so you get the bonus in the lab. If you don't restrict the spell, then the Focus will only apply when you're casting it on males or females, but not in the lab.