** spoiler alert ** 
 I received a free ARC from the publisher 
 You can read this and other reviews at Things I Find While Shelving 
 Woah. 
 Forget a two gender social system. The world of Y Negative is more like a four gender social system. First in the hierarchy are Mascs - genetically male. Next are the Exins who are genetically male but have some genetic abnormalities that makes them more feminine. Then there are Andros - born genetically female, they have surgery to remove their breasts and inject testosterone. Last, Y Negatives, genetic females before they finish their work as surrogates and are allowed surgery and male hormones. 
 It is one fucked up world. To say the least. 
 To me, it seems that most of the Andros we meet inject testosterone and live as Andros more to fit in with society than as a need to be mascs. One of the main characters, Ember, definitely feels more like he is a masc trapped not only in the wrong body but in a society that degrades and uses people like him until they are, basically, nothing at all. It's no wonder that much of Ember's life is given to taking testosterone and working out, trying to make himself as masculine as he possibly can despite his genetics. 
 I almost gave up on this book after the first chapter. Because in this world Andros inject testosterone intravenously which is a HUGE NO NO DON'T EVER DO THAT. Testosterone injections should be intramuscular. Now, this sort of gets explained with regards to black market testosterone, which is laced with (view spoiler)[a drug to keep Andros addicted and injecting (hide spoiler)]. Add to that the fact that black market Testosterone is cheaper than medical grade and the fact that Andros are so low in the social class that affording medical grade is nigh on impossible and, well...You get the picture pretty well. 
 Now, the reason I'm still withholding a star despite the above spoilery explanation is that it's never made clear whether or not medical grade T is injected intravenously or intramuscularly. I'm thinking it's still intravenously which. Well. ehhh. I can't. I can't give you that star back, book. It skeeves me out to think of Andros injecting Testosterone like it's an opiate. Especially since T shots are referred to as shooting up frequently (not just by mascs). I get that, within the world, I do...I just don't get why even the medical grade T shots are intravenous. (If they are?) 
 ETA: I just had a very interesting conversation with the author of this book, who told me about some of the things about Testosterone that she uncovered in her research and how T shots used to be IV instead of IM which, given how backwards this society is, kind of works really well here. So. With that information, I'm upping my rating to five stars. 
 Okay. so now that that *waves hand* is out of the way and y'all know what bothered me, let's get on to the stuff that didn't. Which is most of the rest of the book, so. 
 Ember's life isn't going terribly well. As we already established, he spends more money than is wise on Testosterone. Add to that the fact that his business isn't doing terribly well and, well. You can probably figure that one out. Until a masc named Jess offers him a job - a month out in the wild lands beyond the civilization that's been built up since...whatever happened to this world happened. They need someone to help fix the sensor arrays and what not that they're using to monitor the world and see how well it's doing at putting itself back together. 
 Out in the outskirts with four mascs, things get a lot different. Not only is Ember stuck in close quarters with a couple - Gene and Kacy - who want to ask him questions about surrogacy (a subject which, understandably, isn't something Ember wants to think about) and the type of masc he's used to (one who belittles him simply for being who he is) he also finds himself attracted to Jess. 
 Andro/Masc relationships are reffered to as "het" because of the difference in genetics. And, while not illegal, being het is very much frowned upon. It's considered disgusting for a masc and an andro to be together. So mostly Ember tries to ignore his feelings, but that gets harder when it seems like Jess returns them. 
 During a heavy rainstorm that means they're stuck inside (the rain in this world is acidic and all their power comes from solar panels), Jess and Ember start exploring the possibility of a relationship. Heath is disgusted, so are Gene and Kacy. 
 But there are other problems in the outskirts than just acid rain, wild animals reestablishing themselves, and no gym (yeah, Ember has priorities). There are also people, scavengers who left the cities and live out on their own, stealing what they have to to survive. They try to raid the headquarters where the group is staying and there's a gun fight and things don't go terribly well. 
 (view spoiler)[Ember gets shot. And in an attempt to save his life, Jess gets them both to the scavenger camp, where they basically wind up as prisoners. But Jess has a plan: get a signal off to his father, call for help. And, thanks to Ember's tech savvy, they are able to do just that. But bringing Jess's father into this might save their lives, but it does tear them apart: he definitely doesn't approve of Jess being in a relationship with an Andro. (hide spoiler)] 
 After their parting, Ember has to do some soul searching and self examination. Not just about what he's learned about his hormones, but about everything and who he is and what it means to not be genetically male while still trying to be a man. Is he a man despite his genetics? Does he matter, despite the entire world telling him he doesn't, not now that he's done his service? 
 Is he worth Jess risking everything for him? 
 There are a lot of questions in this book. A lot of interesting things to look at. From Negatives in the scavenger camps who don't inject - one who even goes so far as to look down on and judge Ember for doing so (It can be argued that this is more due to the laced nature of the T, but it read to me more like a judgment against the practice itself, which adds an interesting layer to an already complicated scenario in this book), to the fact that mascs are constantly trying to prove themselves masculine enough. 
 There is so much in this world and it's all so interesting and the author does an amazing job of bringing it all to life. 
 And in the end, Ember and Jess want to change it. And I'd love to find out if they do.