It seems to be a dominant mutation with variable expressivity. Cats carrying this allele, married to females with classic eyes and different races, can produce blue-eyed kittens and small white spots on the extremities of the body.
The amount of white does not seem to be associated with the number of blue eyes (none, one or two). A simple locket very discreet can be indicative of the gene even if the cat has the classic eyes. Moreover, the mutation can be expressed very minimally without affecting the next generation - odd eyes can produce cats with both blue eyes and vice versa.
Marriages between cats carrying a copy of the mutation, with or without blue eyes, can give kittens (homozygotes) almost entirely white, with some colored spots in the lower back, both blue eyes, and deaf. It is important, therefore, to never marry two carriers together, as is already the case for many dominant genes, starting with the white gene W.
Given the risk of deafness associated with these marriages and until we have a test to recognize if a cat is carrying the gene "minimal white and blue eyes", it will be necessary to put in place strict procedures to avoid marrying accidentally two cats of these lineages. It is imperative on the one hand to sterilize / castrate all kittens born of these marriages that will not be used for reproduction, on the other hand to record all these marriages so as to trace all the genealogy.
Finally from behavior point of view, they are cuddly cats, players and pots of glue. They are also talkative and can be handled by young children without leaving any claw. Adorable and funny, Merlin respects this description. He brings the toys back, follows me everywhere and gets on my neck purring whenever he gets the chance.
The gene is not associated with major health problems. And cats with this gene do not have a flattened tail, indicating the presence of the Ojos Azules gene. Recall that the Ojos Azules gene was linked to congenital anomalies, kittens inheriting two copies of the gene being deformed or stillborn. Except this is not the case with the gene "minimal white and blue eyes" inherited by Merlin.
There is nevertheless a risk of deafness, as in white or very white cats with blue eyes. Just like the pigment cells responsible for the color of the eyes and the fur, other cells essential for hearing appear to be subject to the same developmental factors in the embryo.
There is still much to explore in the field of embryology but it seems that if the pigment cells are absent in the eye, there are chances that those involved in hearing are too. This is why deafness is more common in white cats with blue eyes.
In reality the subject is much more complex: breeders of completely white cats manage to produce white cats with blue eyes who are not deaf. Multiple polygenes probably come into play.
These breeders know that if a white kitten has a "kitten cap", his hearing is probably good. This is good news for us because in our case we try to have as little white as possible.
However, given the risk and not having a thorough knowledge of the gene, it is imperative to remain cautious, that is why all our blue-eyed cats will be subjected to the BAER test, to measure the hearing. This was the case for Merlin who achieved perfect results.