Examples of chromosome fusions
You can go to ensembl.org and look up synteny between closely related organisms, like rats and mice.  Below is one example: rat chromsome 1 is made up of all of mouse chromosome 7 and 19, plus parts of 17, 10, and a smidge of 13

https://uswest.ensembl.org/Rattus_norvegicus/Location/Synteny?db=core&amp;r=1%3A126594509-126694509&amp;otherspecies=Mus_musculus