Here in the astrophysic departement when the presures for coherent scientific though become to great we like to relax our mind by perforning what we call redneck genetics. We try to find unlikely combinaison of wedding and children that will make weird things possible such as a single person being both your aunt and your sister (without any incest!).
Since I've got a few minutes let me explain how those two things are possible:
First, the aunt and sister (without any incest!)
First a man must have sex with your grandmother and give birth to your mother then your father in a booth of gerontophily must have a child with your grand mother (your mother's sister) and finally coming back to his senses he decide to talk on the pretty young thing that is your mother and make a child with her.. you. so You now have your aunt (mother sister) that is you sister since she is your father daughter.
Appologies to any redneck that might be offended, we're just playing on stereotype to relax our mind, I'm sure no one think that such a thing happened in the past. ;-) Cheers and try other combinaison you'll see it is fun in a twisted kinda way