I sometimes wonder if "I" would have existed if another sperm had fertilized the egg that was to become "me". Is this even answerable in any meaningful way? I sit here and experience myself as a unique individual and I speculate that everybody else feels the same about their own unique consciousness and self-awareness. So if a different sperm had fertilized the egg that was there when I was conceived, would "I" have come into existence nine months later, but with a different set of genes?
Studies tend to show that about 50% of variability in behavioral traits is explained by genes and 50% by environment. Unlike with identical twins, your other could have a pretty similar experience to you. So, with 25% of your genes different, your other would be up to about 8x more similar to you than a random person is, and would have many of the same experiences and memories.
But of course that very-similar-person's consciousness wouldn't be yours; you are by hypothesis not around to experience anything. You can't really arrange it so you can without breaking the whole premise. So the other-you is identifiable as the most you-like entity in that hypothetical universe, and that is about as far as it goes.