Note This article was written by conny of cattery rivium to wich i added some information. Conny said i could use this for my own website about odd eye. She stopped breeding and wanted this information to be passed on. I have tried as good as possible to translate into English, I would like to apologize in advance when it is not all correctly translated.
I also want to mention that I and conny are not geneticist. We 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 room or thought when we see that there are also cats without white odd eyed, this indicates how little we know so far about 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 in the eyes.
A side-effect is that cats with decreased melanin production coul have a coat that is not always correctly colored like the breed standard desires. It is common for odd eyed cats , or cats why carry odd eyed to have a white tail tip. See the above picture of Rivium's Kissable, a cinnamon white girl with a clear white tip on the tail. (picture 3)
The tail rarely also has a kink, this can vary from: a small kink 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 could be a connection between the odd eye-gene and kink tails, however research has not yet clearly found out why.
At fully white cats (photo 4) is linked to the genetic factor W (dominant white) This gene can turn of color in the fur and eyes. White cats can have deafness or hearing impairment. At colored cats with white in the coat (bi color,harlequin, van) there are no cases for deafness.. In colored cats the pigment is 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 color for the eyes yet. All kitten are born with blue eyes. At the age of three or four weeks kittens start to create melanine, this melanine is slowly given the eye his color. In odd-eyed cats the pigment production is 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. Darker colored cats seem to have the eyes change faster as lighter colors. Red and creme cats seem to have sometimes a slower change of eye color. The eyes remain a longer time blue as other kittens with other colors of the litter.
Odd eyed in white cats inherits dominant , it means that only one parent need to pass it on to her/his offspring. Only the white borns can be odd eyed, unless the white cats has also other odd eyed bloodlines in the genes.
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 inherited 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 be odd eyed because the dominant inheritance rule of white. All kittens out of this combination carry the bi color cat his odd eyed gene, also the white born kittens from this combination will carry the bi color odd eyed gene. Therefor the white kittens can give odd eyed cats with color when mated to another odd carrier later.
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 these odd eyes are 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, normal bi color (tricolor in odd eyed photo 8) is only since 2019 register by FIFE. It's also recognized in LOOF and WCF. Solid odd eyed is not yet registered and will get RIEX (experimental) pedigree. (Photo 9)
Solid odd eyed cats are very rare. Normally there should at least be one hair white , to be odd eyed. The genes of the white (lack of color) gives also the lack of color in the eyes.
It also seems that cats with much silver in lines , give more odd eyed (some breeder believe the same about point cats in the bloodline). Also cats with the coat itself in silver or smoke , more often seem to have a much more darkblue eye color. I saw this multiple time in smoke cats, but it is not always the case. The pictures below are examples.
black smoke blue eyed born with yvie die cinnamon smoke blue eyed
Hillya de candybelle choc smoke bicolor odd eyed The same cinnamon smoke blue eyed as above on adult age.
Another possibility in the eye colors are split , or cracked eyes. These eyes have both orange as blue in them. On show they are not appreciated as much as odd eyed (in theory the eye should completely be blue or orange, but not both.) Personally I find it beautifull. Look at pictures below.
British gems Sophie : split odd eyed at both sides.
British gems badger, who has a blue drop in his orange eye.
Marilyn , owned by lilian achille fould (british de candybelle)
British shorthair with both eyes crached , the blue and orange flow into each other
Blue eye cracked with a part of orange
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 important role in the transmission of the 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.