phoenix, it's epigenetics. It's a newish field of study, but broadly, it is to way genetics and environment interact. The theory is that much of our genetic material isn't simply 'there'. It can be activated or lie latent, depending on the environment around the foetus as it develops. So, a mother who incubates a donor egg is providing her own unique biological stamp to shape some of that resulting baby's characteristics.
Also - and this is totally personal, but might be helpful - I thought I would very much be at a disadvantage that my DD wasn't biologically connected to me. It worried me. And I thought that, even though I was happy to be her mother, it would be a harder bond for me to forge, as she wouldn't be biologically mine.
She is only 11 weeks old and already it does not feel that way at all.
I do get where you're coming from, though, as it seems extremely unlikely DD will share a sperm donor with any future child we have, and that makes be inexplicably and irrationally sad. I am sure that I would not care once that future baby were here (if we get that far). But I understand the emotional reaction, and I know first-hand that it is possible to find your emotions shift.
Please don't feel I'm trying to tell you you should feel any certain way - I'm not - but I'm sharing my experience in case it is of any use at all.