Semen, not sperm, I believe. So the man is a chimera (he has his own DNA and the donor's DNA in his body). His sperm is still his own DNA, but his semen contains the donor's DNA. His semen should therefore contain BOTH his DNA and the donor's DNA ... but to make matters a bit more complicated, he's undergone vasectomy so he no longer produces sperm. Thus his semen only contains only his donor's DNA. Yeah, complicated!
Hark! Methinks thou hath a good point though Shakespeare is probably spinning in his grave to hear us modern English speakers butcher the Queen's English.
So the man is a chimera (he has his own DNA and the donor's DNA in his body). His sperm is still his own DNA, but his semen contains the donor's DNA.
His semen should therefore contain BOTH his DNA and the donor's DNA ... but to make matters a bit more complicated, he's undergone vasectomy so he no longer produces sperm.
Thus his semen only contains only his donor's DNA.
Yeah, complicated!