This article is from the WSSF 2015 AFRMA Rat & Mouse Tales news-magazine.
Mosaic is from 1 egg that has different cell make-up from a spontaneous mutation or error in the cell during embryo development.
Chimera is the fusion of 2 eggs with different cell lines
(e.g. Seal Point with Blue Point so parts are brown and
parts are blue). They can also be when an animal contains
cells from another animal. A Chimera is from the Greek
mythology where one animal was comprised of 3 different
animals. You can see examples of cat chimeras on the
Tortie Tomcats: Chimeras
(down towards the bottom of the page is a photo of a Ragdoll that has the legs
on one side of his body blue and the other side of his body
You can also check out these pages:
Some sources/people use the terms interchangeably but they are two different things.
See also the AFRMA Tidbit