Madara
TRANSPLANTED his eyes to nagato thus making him have both senju and uchiha
DNA. He did this, stated below by Direcorpse, because the uzumaki clan are related to the senjus.
No, let me fix that.
Kakashi was implanted with the sharingan but why does he not have uchiha DNA in him??
Transplanted and implanted are different. Read this to get a better understading of what madara did:
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. Either Kishi doesn't want to tell us how the transplantation was done or he wants us to do our own research on how the process is done, but we can say madara transplanted something from his body along with the rinnegan