I'm a bit uninformed on this; it seems fascinating. Do these things happen due to something unusual during the growth of a fetus? What's the name for this phenomenon?
Moron here: Are XY females sterile or is it possible for them to pass on the Y, along with a male partner Y gene to give the baby YY genes? Or is this combination non-viable and wont develop?
XY females aren't always sterile! Most of the cases we know of are sterile though, because you don't get tested for this stuff unless something's wrong (the woman in the case study got tested because XY women are common in her family, her daughter is XY).
Mothers always pass the X chromosome due to how the egg works from what I remember. The sperm determines whether you get x or y for the second part.
There is a rare event where you can have multiple sex chromosomes, like XYY, but the X is always present (at least for humans). Considering the genes in an X chromosome are vital to life, even if we could artificially create YY, it would probably end up nonviable