Apparently, with Orphan Black, sexuality is NOT something you are born with (as they are all clones, with little variation).
In fact, science suggests that sexual orientation is determined, not by genes, but by developmental conditions in the womb, such as the ratio of sex hormones that the developing fetus is exposed to. So it
is something you're born with, but what we're born with is shaped by far more than just our DNA. In recent years, we've begun to discover the importance of epigenetic factors in determining how our genes are expressed. The DNA is the basic set of instructions, but it doesn't exist in a vacuum; it's surrounded by all sorts of proteins and enzymes and stuff that mold it into a certain shape, make some of its genes more accessible and shunt others into the background, etc. So a single set of genes can be modified in a variety of different ways by epigenetic factors. There has been dialogue in
Orphan Black about epigenetics as a factor in the diversity among the clones.
But being intense/passionate (rather than an even handedness like May is portrayed in Agents of Shield) seems to be a common trait of the clones.
I hesitate to generalize like that, precisely because it is overly simplistic to assume that DNA alone dictates everything about a person. Behavior is also something that can be shaped by developmental factors before and after birth, such as the extent to which the development of certain structures or connections within the brain are encouraged or inhibited, not to mention the conditions of a person's upbringing.
So far, Rachel seems like a very cool and controlled individual. And Cosima seems much more laid back than Sarah or Allison (though maybe that's a function of her marijuana use).