Hello, I have recently discovered that I have a sister from the same father but a different mother. What matters more? Being born from the same mother or from the same father. I have 2 half brothers from the same mother and we are nothing alike, buuuuuut they are. My half sister from the same father and I however are totally alike. She has 2 half sisters from the same mother but different father.
Each egg has 23 chromosomes. Each sperm has 23 Chromosomes as well. However, these chromosomes from either egg or sperm are NOT identical and there is tons and TONS of variation in every single egg and sperm. So it really doesn't matter. Every egg, every half sibling on your mom's side has different genes and chromosomes that she personally supplied. The same goes with your half siblings on your father's side. There are some similarities with every sibling, but honestly even if all your siblings shared the both parents with you-NOTHING is the same unless you have an identical twin.
Personally I have 5 half siblings. My two eldest sisters who share my father, I never talk to. However I do have some facial similarities. My three other older siblings I share a ridiculous amount of similarities with, ignoring the fact that they have a different father and spent every summer away from me and my mother to live with him. And honestly this starts to argue Nature over nurture. Do we have similar humor because of our shared mother, or because we grew up together? Either way my eldest half brother and I have identical hair color and very similar eyes. Our blood doesn't match up at all though- that's the fun part about knowing differences. Their father is O +/- or O+ and our mother is A+/- or A+. My brother is definitely A/O +/- and that's easy simple genetics that .. well honestly would be easier to explain if I drew it all out but having this kind of variation can be really interesting from a scholarly perspective.
Now if you're asking about medical history honestly it gets complicated here, but I still take in all their medical info- alcoholism, cervical cancer, arrhythmia, depression- and call it family history. It's hard to know where this is coming from -our mother's side or their fathers, but if I assume I'm at risk and watch for it. It won't matter if I'm wrong, because I'll be prepared and hopefully catch anything early.
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