Note: i have written a article for my own website about odd eye, i have tried as good as possible to translate into English, I would like to apologize in advance when it is not proper English.
I also want to mention that I am not a geneticist. I wrote this article after research and from personal experience .
A cat with odd-eyed eyes is an animal with one orange, yellow or green and one blue eye. Most common are the fully white cats with this special eye color, but it is also seen in cats that are predominantly white in color with only a few colored coat parts; by (photo 1), harlequin/van and, to a lesser extent the normal bi colors (photo2), in very extreme cases we can find odd eyed in cats without white. In the case of cats without white in odd eyed, the cats I've seen where always black cats, in my opinion this has to do with the silvergene, this is just my opinion that i cannot explain. Because we assume that a cat has to have at least once the white-gen (S) to be odd eyed, it still gives plenty of food for thought when we see that there are also cats without white odd eyed, this indicates how little we know so far of the genetica of odd eyed.
Odd eyed at bi color cats is an autosomal defect, in my opinion a defect is not necessarily negative. In the case of the odd eyed cats it is where we select on the defect of the lack of melanocytes.(Melanocytes are pigment cells that make pigment granules, the pigment of those grains is called melanin)Blue eyes are caused by the lack of the melanocytes.
A side-effect is that cats with decreased melanin production the coat is not good coloured, in diluted colors it is less clear than in undiluted colors. It's so that when the odd eyed cats, or cats that have the odd eye-gene often the point of the tail is white, see the above picture of Rivium's Wolf, a cinnamon white longhair young male with a clear white tip on the tail.
The tail can also have more or less kinks, this can vary from: a small kinks at the point of the tail, a tail that is carried flat on the back (flat to back tail), a tail that is worn slightly curved (aerial curled tail), a curly tail that is carried sideways (flank curled tail). It seems there has to be a connection between the odd eye-gene and kink tails, however research has not yet clearly see why there is a connection.
At fully white cats (photo 3) is linked to the genetic factor W (dominant white) that the pigment inhibition in fur and eye or eyes can turn off. White cats can have deafness or hearing impairment. At colored cats with white in the coat (bi color,harlequin, van) will be no deafness . Here is the pigment inhibition associated with the dominant gene S (piebald white spotting).
Kittens are born with a baby-blue eye color, newly born kittens did not created the dey. At the age of four weeks kittens started to create melanine, this melanine is slowly given the eye his color. In odd-eyed cats the pigment production slowed down in one eye.(Melanocytes are pigment cells that make pigment granules, the pigment of those grains is called melanin). Blue eyes are caused by the lack of the melanocytes. The eye color is determined by the genetic material into the body cells. This material is on the DNA that determines which substances are activated to form an eye color. A substance that is created is among other melanin. In cats with dark colored eyes is much melanin created, in cats with light eyes is very little melanin. Melanin is also find in the hair.
Odd eyed in white cats inheritance dominant rules, it means that only one parent need to passe it on to her/his offspring, only the white borns can be odd eyed.
Odd eyed at bi-color cats is an autosomal inheritance defect, the "odd eyed gene" must come from both parents, cats can carry this gene (or defect) for generations, I would like to say that there is no such thing as one odd eyed gene, the eye color is an inherited trait that is determined by multiple genes. In autosomal recessive inheritance, both parents has a gene-defect (the gene for odd eyed) and is given on to there offspring , the kitten has inherits from both parents the odd eyed gene.
When the goal is to breed bi color odd eyed cats it makes little sense to breed a white odd eyed (or white odd eye carrier) with a bi color odd eyed (or bi color odd eye carrier), bi color odd eyed kittens will not be born from this combination, these are two different genes. White born kittens can of course odd eyed because the dominant inheritance rules, all kittens out of this combination carry the bi color odd eyed gene, also the white born kittens from this combination will carry the bi color odd eyed gene.
Odd eyed or two blue eyes is currently the most rare that you can find at the British shorthair. Bi color odd eyed cats have NO hearing problems, because this odd eyes be bred with bi colors and not about white cats.
Please note that odd eyed cats in Van and harlequin's are recognised by all cat associations, bi color odd eyed is much rarer than the van or harlequin odd eyed, but a normal bi color in odd eyed (photo4) is not recognised by FIFE. It's recognized in LOOF and WCF.
Why there is no dna test:
A cat has 48 chromosomes (19 pairs), each chromosome is formed from a strip of DNA, which consists of thousands of pieces, called genes. Chromosomes contain all genetic properties. DNA is located in the nucleus of each cell, actually in the chromosomes in the cell nucleus. A cat has more than 80,000 genes.
The first cells in an embryonic kitten grow into many different cell types. During this development, the cells get their specific function. They develop into brain cells, skin cells or muscle cells. Each cell contains a complete copy of the genetic material of the parents, in the form of chromosomes. With each cell division, a copy is made of all the genetic material. Chromosomes are the carriers of the genes. The chromosomes contain all the genetic information that is necessary to develop, maintain and reproduce an individual.
You can see chromosomes as long strands. These consist of a substance that we call DNA (deoxyribonucleic acid). The DNA contains the code where all our inherited characteristics are recorded.
A gene is a piece of defined DNA that contains the information for the formation of a particular protein. Proteins go to compounds with other proteins and therefore have multiple functions in the body. Genes determine the genetic characteristics, such as the color of the hair and the eyes.
Until now, geneticists have found at least 15 different genes which play a importaint role in the transmission of the (human) eye color.
DNA studies examines differences or similarities between sick and healthy genes. For defects caused by just one gene mutation can be developed a DNA test, when multiple genes play a role, as in odd eyed, the possibility of a DNA test does not yet exist.