A blog by spcaLA president, Madeline Bernstein

Mar 19, 2012

Tortoiseshell Cats Cannot Be Cloned

courtesy Google Images
The ability to genetically engineer food animals, replicate disease free humans and clone your favorite pet have been the fodder for science fiction films as well as for very real debates about the ethical issues attendant when  humans create life. There was quite a stir when a man paid $100,000 to a South Korean laboratory for a genetic replica of his beloved dying dog, as the science involved is not perfect and so may dogs are waiting in shelters for homes.

Well nature has found a way to thwart science in the case of tortoiseshell cats! These cats will not be cloned! The tortoise color comes from one red gene and one black gene that reside in the cat X chromosomes. Due to a process where the developing embryo cells randomly select and deactivate an X chromosome a cat can be black, red, or tortoise - black and red. There is no set blueprint that governs the cells in this process. The cloning procedure takes DNA from one cell which will have only one color. The cats are so stubborn that even if scientist takes a cell before the random deactivation occurs it ultimately occurs anyway and affects the color of siblings. A clear explanation can be found in 109 science publication:

“Tortoiseshell cats are the result of two different genes teaming up. One gene will turn the cat red, a nice solid ginger. The other will make it a black cat. Each gene is inherited from one of the tortoiseshell’s parents. Each is on one of the tortie’s X chromosomes. The tortoiseshell look is produced because of a process called ‘X-linked inactivation.’ The cells of developing embryo of the tortoiseshell cat randomly shut off one of the X chromosomes. And there’s no general consensus among the cells about which one to switch off, so each cell simply picks one. This random shut-off is why tortoiseshells have an unpatterned mix of black and red hair over their bodies.
Cloning a tortoiseshell involves taking the DNA from one cell. Since each of the cells have only one active X chromosome, when a new tortoiseshell embryo is developing using the borrowed DNA, it only has one gene affecting its coloration.
Thus, a cloned tortoiseshell kitten will generally be either black or red. Even if someone were to nab a cell from a developing embryo before the X-linked inactivation happened, the new cloned kitten would also randomly inactivate its X chromosomes, leaving two cloned siblings that don’t have the exact same color pattern.” 

There you have it. I am reminded of this exchange from the film Jurassic Park (1993):

Henry Wu: You're implying that a group composed entirely of female animals will... breed?
Dr. Ian Malcolm: No, I'm, I'm simply saying that life, uh... finds a way. 


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