What makes a cat’s fur white? And what makes a cat’s eyes blue? And white cats deaf? I am not referring to albino cats by the way.
White fur
White fur contains hair shafts in which there is no pigment called melanin. White is the absence of colour. Technically you might say that white fur is transparent but it’s too opaque to be transparent. I guess that this is the keratin (a protein) which makes the fur and which is not transparent entirely transparent.
Normally melanin is injected into the hair shaft by a melanocyte cells (pigment producing cells) in the bulb of the hair shaft. As the hair shaft grows the melanin pigmentation is injected into the hair shaft.
When the fur is white there are no melanocytes in the hair shaft bulb. The hair shaft bulb is the cavity at the base of the hair shaft. The reason why there are no melanocytes in the hair shaft bulb is because they failed to migrate from their point of origin when the embryo was developing to these particular sites in the skin.
And they failed to migrate to their normal positions because of the presence of one of two genes: the dominant white gene (w) or the piebald gene (S) otherwise known as the white spotting gene. The latter is responsible for small or large patches of white fur (‘spotting’) whereas the former causes complete whiteness.
It is these genes which interfere with the normal migration of melanocytes. Because there are no melanocytes there is no pigmentation and the hair shaft is empty.
Eyes
With respect to the eyes, these pigment producing cells called melanocytes normally circle the circumference of the iris injecting colour into the iris. Once again, if there are no melanocytes in their normal position because of the presence of the genes mentioned, there will be no pigmentation in the iris.
When there is a lack of pigmentation in the iris the eye colour is blue because of the refraction of white light from ambient light and from the sky. The cornea and iris refract the light removing all colours except blue. The process that makes the sky blue is similar. The sky is blue because of the scattering of light rays. Blue light is a short wavelength and therefore it is scattered more. In respect of cat eyes, it is ‘refracted’ more with the same end result; making blue light visible.
P.S. Kittens have blue eyes because the creation and migration of melanin in the iris takes the first months of the kittens life to complete.
Ears
There is a spin-off from the presence of the dominant white gene. It can cause deafness. Pure white cats are often deaf.
RELATED: What percentage of white cats are deaf?
If the melanocytes do not migrate to the ear, the ear canal remains closed. As it is closed the cochlear (part of the cat’s anatomy where sound waves are converted into nerve impulses) does not perceive a blood supply and it degenerates. The nerve cells of the cochlear die causing permanent deafness. We don’t know the exact cause of the vascular degeneration but it is linked to the absence of melanocytes in the blood vessels.
If a white cat has normal coloured eyes, it is unlikely that they will be deaf. If a cat has one copper eye and one blue eye, the ear on the blue-eyed side may be deaf.
I hope this helps. Please leave a comment if you want more.
