The Tortoiseshell occurred some time after 1962. The Tortoiseshell is sex linked and all Tortoiseshell hamsters are female. The Tortoiseshell is a bi-coloured hamster being a mixture of two colours using the Yellow gene. The coat of the Golden Tortoiseshell is a mixture of patches of golden-brown with grey roots (Golden) and patches of creamy yellow (Yellow). Often there is some brindling between the two colours. The eyes are black (as with the Golden) and the ears and dark grey (as with the Golden).
It is possible to produce Tortoiseshell in other colours, for example Cinnamon Tortoiseshell where the hamster has patches of Cinnamon colouring and a honey-yellow colouring. In this instance the eyes are red and the ears are flesh coloured as they are with the Cinnamon. The most striking Tortoiseshell is the Black Tortoiseshell.
Tortoiseshell hamsters are female as the Yellow gene is sex linked but very occasionally a male Tortoiseshell is produced when a male hamster contains 3 sex chromosomes (two female chromosomes and one male chromosome) instead of the normal two.
In the US the term "calico" is sometimes used for Tortoiseshell hamsters.
The Tortoiseshell can be combined with any coat type, and can also be combined with a pattern such as Banded to produce a tri-coloured hamster.
For showing the Tortoiseshell should have equal amounts of colour and "yellow" and the Tortoiseshell and white should have equal amounts of colour, "yellow" and white. The borders between the colours should be clearly marked with little or no brindling.