Does a mule have by definition a diploid (2n) genome or 1n + 1n haploid genomes?

Hi! If you mean the hybrid between a horse and a donkey, then the correct term is "2n" (diploid). We only use "n" to mean haploid nuclei, as in for example fungi. Writing n + n would mean two genetically different haploid nuclei within the same individual (as in some fungi), but that is not the case in mules. Mule cells have all of their genome contained within a single diploid nucleus.

Does that help?