Heterochromia

I’d never seen a dog or a cat with mismatched eyes until I started as a volunteer at the Dogs’ Refuge Home. Of course, I’d seen them on TV and in magazines, just never in the flesh.

The first dog I met with odd eyes was Harry. Harry is a Kelpie x Heeler with one light blue eye, and another that is brown at the top, and blue at the bottom. Just gorgeous!
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The next dog that I met at the Refuge bearing mismatched eyes was Thor. Thor is a Siberian Husky cross. His right eye is blue, his left is brown. Another amazing dog.
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The third dog with odd eyes is Brittney, who uncannily resembles a fox, complete with catlike body and a brush tail. She’s also a Husky cross, but I rather fancy there’s some Australian Dingo in there.
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So, what exactly is the scientific explanation for these beautiful eyes?

It’s called Heterochromia. Here’s a bit about it from Wikipedia:

In anatomy, heterochromia (ancient Greek: ἕτερος, héteros, different + χρώμα, chróma, color[1]) is a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin (a pigment). It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury.[2]

Heterochromia of the eye (heterochromia iridis or heterochromia iridum) is of three kinds. In complete heterochromia, one iris is a different color from the other. In sectoral heterochromia, part of one iris is a different color from its remainder and finally in “central heterochromia” there are spikes of different colours radiating from the pupil.

Though multiple causes have been posited, the scientific consensus is that inbreeding is the primary reason behind heterochromia. This is due to mutation of the genes that determine melanin distribution at the 8-HTP pathway, which usually only become corrupted due to chromosomal homogeneity.[3]

Eye color, specifically the color of the irises, is determined primarily by the concentration and distribution of melanin.[4][5] The affected eye may be hyperpigmented (hyperchromic) or hypopigmented (hypochromic).[3] In humans, usually, an excess of melanin indicates hyperplasia of the iris tissues, whereas a lack of melanin indicates hypoplasia.

I had a look on Pinterest and found these other beauties (below). You might be asking if the condition only affects dogs and cats, as there’s a predominance of them here…the answer is no. Heterochromia has been observed in horses, cattle, ferrets, monkeys, chimpanzees. Quite possibly the reason we think it’s only dogs and cats that exhibit this genetic mutation is because dogs and cats are domesticated animals who live alongside humans in their homes, and we have more daily contact with them than say, with a chimpanzee. Therefore, the more popular something is, the more it appears in our consciousness.

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