Does gender matter?

In my sociology class we have been talking the past couple days about gender. I have learned that ones gender does not relate to ones sex. For example we talked about how a boy playing with a girls toy makes the boy seem wrong and different but when the girl plays with a boys toy it's alright and she is just called a tomboy. I steped out of the box of society and looked around for this in my everyday life. A matter a fact it was happening in my own house. I have 3 sisters and 2 brothers and one is older and not around much so it's just us 4 girls and my one little brother. There are so many girls toys just laying around the house and toys that we play with all the time. My brothers friend came over to play the other day and my brother asked if he wanted to play with the Dora and Diego house that was my sisters. My brothers friend said "no I'm not a girl!" I felt bad for my brother because he liked playing with the house with my sisters. The other boy I could tell was raised up in a home where it is not ok to play with the opposite genders toys. I beleive that anybody could dress or play with whatever they want to.