tortoiseshell

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tortoiseshell 

Material used in the manufacture of spectacle frames. It is obtained from the shell plates of the hawksbill turtle. See plastic spectacle frame; spectacles.

tortoiseshell

a coat color in cats consisting of a mixture of black and shades of red to yellow, usually broken into large patches. The color can be found in a variety of cats, both long- and shorthaired, and specific breeds, such as Burmese. Tortoiseshell-and-white is another variety, called calico in the USA and chintz in the United Kingdom. Because the genes for black and orange (including shades from red to yellow) are carried on an X chromosome, but not the same one, only females can carry both colors. Males from similar breeding are either orange or black. There are isolated examples of tortoiseshell or tortoiseshell-and-white male cats, but almost all are sterile due to the chromosomal abnormality of XXY. These are considered models of the human condition, klinefelter's syndrome. Rarely, the phenomenon may be attributed to somatic mutations, crossing over of chromosomes or mosaicism.