OK so quick back story, I have a daughter from a previous relationship and am currently with a different guy with a few kids who are all boys and one potential girl. He thinks the girl could be his brother's and that's why she looks like him. So he claims her but isn't positive.

Any who, so I'm pregnant now to this guy with a baby girl. He thinks its not his because-and I quote *in self-righteous tone*, "I only make boys!" Like his sperm is too rich to produce girls and boy's are more important or some shit. Now I think he's a bit of a dipsh*t and don't believe this to be true at all.

For the record the possibility is there that its the above mentioned Ex's but I'm not sure. I'm only throwing that detail in because I thought it might be vital to my question...

The point I'm getting to is how is the sex of a baby determined? By man or female or is it a toss up? Is it possible that indeed a man can only makes boys?