Good example of sectoral heterochromia in a white domestic cat

This is a beautiful white cat with a not untypical eye colour. It looks unusual but it really isn't that unusual. It is a variation on or an extension of heterochromia iridis in domestic cats which in layman's terms means odd-eye colour. This is what happens.

Good example of sectoral heterochromia in a white domestic cat. Image: Pinterest.

The dominant white gene produces an all-white cat by removing melanin from the hair strands to leave them a sort of opaque-white. The gene affects the migration of melanin producing cells called melanocytes in the iris of the eye.

This can leave the eyes of an all-white cat with the colour blue. This is not because there is blue melanin pigmentation in the iris but because there is no pigmentation. The blueness comes from the refraction of white light through the eye. 

The colours of the rainbow e.g. red, are scattered less than the colour blue as they pass through the eye because they are longer wavelengths. Blue light has a shorter wavelength and is scattered more leaving the eye the colour blue. 

Kittens have blue eyes until about 6 moths after birth as the melanin producing cells create melanin for the kitten's iris.

And sometimes one eye is affected like this and the other isn't which leaves the odd-eyed appearance. This normally means one eye is blue and the other is yellow. And sometimes in the case of sectoral heterochromia that odd-eye colour takes place within a single eye which, means that half the eye is yellowy brown and the other half is blue. Once again this is about the migration of melanin producing cells affected by the dominant white gene.

The dominant white gene also affects hearing. It affects the functioning of the inner ear in the way the nervous impulses are transmitted from the cilia in the semicircular canals to the brain. The theory is the cilia (fine hairs) of the semi-circular canals are missing or partially missing because of the dominant white gene. 

The end result is that the cat becomes either deaf in both ears or deaf in one ear. And if they are deaf in one ear it is on the side where there is a blue eye.

RELATED: Sectoral heterochromia in cats.

Comments are welcome. Wrong? Please tell me.

Phenotype and genotype of tabby cats

The picture shows the phenotype and genotype of tabby cats. "Phenotype" means the physical characteristics of an organism, in this instance, a domestic cat and the word "genotype" means its genetic makeup. The genes that make the tabby coat are shown in this image. There is a certain way of symbolising genes as you can see. Read more about the tabby cat by clicking on this link and this link for info on tabby cat coats.

Pictures: Helmi Flick with her permission.

Is cat genome sequencing a precursor to more experimentation on cats?

We are told that the cat genome has been sequenced. The impression given is that this is a major step. What is genome sequencing? I don't exactly know to be honest but what I do know is that it does allow people to better understand the building blocks of the animal of which the genome has been sequenced and it also allows scientists to better understand the genetics of the animal, as I understand it.

In this instance an Abyssinian cat living at the University of Missoula in Colombia was the subject chosen to represent her species.  A 25 man multinational scientific team was pulled together to sequence the cat genome.

It is stated on the website that provides the source of this information that one reason for sequencing the genes of the cat is to better understand disease, at least in theory. Although cats and humans don't infect each other with their respective diseases except on rare occasions, domestic cats are known to suffer from about 250 conditions which are “analogous to human conditions".

One of them is feline AIDS (FIV) caused by a virus which depresses the immune system.  Accordingly, “feline infectious agents offer powerful natural models of deadly human diseases".

Those words indicate to me, possibly incorrectly, that scientists have recognised that many diseases that affect the cat take a similar course to diseases that affect humans and therefore testing medications on cats may help scientists to better understand how to cure human diseases.

I'm just throwing up a red flag to see where it lands but I don't see any reason to sequence the cat genome other than if it has some benefit to people because that is how people think. Already we know that cats are used in medical testing, although of course, far more rarely than mice, for example.

I hope I'm incorrect.

Mediterranean Cats

Mediterranean cats are often white, short haired, slender, with Van-type markings and sometimes they have odd-eye color because of the presence of the while spotting or piebald gene. The medical term is heterochromia iridum.

Having looked at a lot of cat pictures, the above description is quite typical of Mediterranean cats. I am thinking mainly of the Greek Islands and surrounding areas. That is not to say that a lot of other coat types can't be seen as well. You will see a wide range. It is just that this type is fairly typical. You'll see Van-type cats in Morocco too.

Mediterranean cat - Odd eyed cat - photo by ihasb33r (Flickr)

The above picture is a slightly cleaned up version of the original that was taken on Greece as far as I can tell. It is a nice picture, particularly when cleaned up a bit (my personal opinion). That's why I picked it and thanks to the photographer for the license to publish here.

For me the look is so typical of Mediterranean cats. Quite delicate in appearance and size. That is probably due to the heat. Warmer climates tend to produce smaller cats and colder climates produce larger cats (the Sumatran and Siberian tigers are examples).

The genes that have caused the coat are the same as those that produce the Turkish Van pattern in neighboring Turkey. No surprise there as the countries are adjacent to one another. The picture perfect version of the van pattern is an inverted black "V" shape on the forehead and over the eyes and a black tail.

This little cat has a vestige of that. Blue eyes are due to a lack of pigmentation that was removed by the same gene that removes the pigmentation in the fur - the piebald gene. It is the same gene that produces the painted or piebald horse.

Greek cats are not treated that well it appears. A new cat breed is being created in Cyprus. Also you might like to read about the spread of the various cat breeds from the original source.

Agouti gene - what is it?

The agouti gene is probably the best known of the genes in the cat breeding world (the cat fancy). It is one of genes that is responsible for the tabby cat. If a cat has banded or ticked hair strands the cat carries the dominant agouti gene symbolized by the letter A. This gene signals the creation of the dark and light agouti banding on each hair. Alternately the non-agouti gene (a/a) signals the creation of solid colored hairs.

The agouti gene signals the on-off creation of eumelanin a pigment produced in a cell called a melanocyte. Eumelanin is black-brown in color. When the agouti gene has not signalled the creation of eumelanin a pigment called phaeomelanin is produced in the melanocyte. Phaeomelanin is red-yellow in color. The melanocyte feeds the pigment into the hair follicle.

Tabby cat hair strand showing banding of pigmentation

The message (signal) to create these two different types of pigment is effected by the action of a protein molecule called the agouti peptide and a hormone called the Melanocyte Stimulating Hormone (MSH).

The tabby gene dictates how the hairs are positioned throughout the body so it dictates how the tabby pattern appears. It works in conjunction with the agouti gene to create the well known tabby cat of which there are three types: classic blotched, spotted and mackerel or striped.