I think it is pretty clear that they are Talking about the Y chromosome, i.e. being born a different gender.
There's far less than one chromosome's worth of difference between me and a orangatan.
"Just a chromosome" is like saying "just an extra brain"
Anyway, it could be interpreted as "If my parents had a girl instead of me, what it would be like to be she".
I don't like when correctness is sacrificed for emotional engagement.
My understanding was that when people make "If I were X" statements, they are referring to having a conscious experience different than what they are currently experiencing. They would still be themselves by virtue of being the conscious observer in that context.