I'm assuming we both agree that Creative Spark is tied to spirit and soul, and thus identity. In itself, the existence of transdimensional counterparts is a stage for the age-old philosophical dilemma of what individualizes a person?
The question is not unanswered, though.
Establishing Creative Sparks as being connected to genes is not meant to suggest that a person's self is based only on genes. A person's self is established by, among other things, past present and future, including potential to make different choices. Just as genetically identical twins are different people, genetically identical counterparts are different people. Even if they share experiences, genes, creative sparks, they are different people. Clones are different people. The phrase, "I am you." is in many ways incorrect.
I'll also address that minor differences in phyical traits, like curly hair, are small changes but the genome at large remains largely similar. In Aiden and Lost's case, even with one chromosome (X vs Y) being entirely different they suggest (and in-universe there is basis for it) that their souls are similar enough that in the subconscious process that a soul interfaces with a body, when Future Aiden's physical self was destroyed his Creative Spark erroneously identified Aiden's and Lost's physical selves as its physical self, only to be repulsed as they were already occupied, before attempting to respawn himself.