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These gorgeous rodents here are Chimera or mosaic rats

there tri-colouring is caused by genetic mutation or the fusing of two fertilized eggs in the womb

"An animal chimera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction. If the different cells have emerged from the same zygote, the organism is called a mosaic. Chimeras are formed from at least four parent cells (two fertilized eggs or early embryos fused together). Each population of cells keeps its own character and the resulting organism is a mixture of tissues. There are some reports of human chimerism.” [X]

However because this these rodents are very rare and most cannot breed, even if they could, chances are none of their offspring would exhibit these tortoiseshell/calico like colourations!