An adorable litter of four white tiger cubs was born recently at Japan's Tobu Zoo, on the outskirts of Tokyo. But hold the squees! You won't find cubs like these at zoos in the United States for reasons that might make you wince.

White tigers are often billed as a rare variety of tiger, but they are not a distinct subspecies. The animals are really Bengal tigers (Panthera tigris tigris) with a rare recessive gene that gives them a striking white coat. Highly selectively breeding (read: lots of inbreeding) is often necessary to ensure that this gene is expressed. This can lead the tigers to be cross-eyed, or have congenital defects like misshapen skulls or a cleft palate — traits that would make it hard for them to survive in the wild.

For that reason, the American Zoological Association has banned its member institutions from breeding white tigers, lions and cheetahs.

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