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The original post: /r/askscience by /u/Akira3kgt on 2024-10-10 17:28:55.

If chromosome fusion occurs as a single event in one generation, and organisms with different numbers of chromosomes generally don't produce viable offspring, then who would this organism with newly fused chromosomes produce offspring with?

For example, in the human genome when chromosome 2 formed from the fusion of two other chromosomes, who did this newly fused unique organism mate with?

Is it simply that they usually don't produce viable offspring but in some rare cases they do? If so, then maybe this fusion happened more than once and it took many attempts at offspring before it caught on and a viable offspring was produced?