White Cats: Odd-Eyed and Otherwise, Cat Fancy vol. 1 no. 1
CAT FANCY's first issue took a look at white cats and their mystique.
Rosemonde Stevens Peltz |
From the Archives of Cat Fancy: Enjoy this all-access pass to cat history from the pages of the oldest living cat magazine. This content remains in its original form and reflects the language and views of its time. Health and behavior information evolves and only the most current advice should be followed.
A photo from CAT FANCY's first issue, which profiled odd-eyed white cats.
Excerpted from CAT FANCY magazine, 1965, Volume 1 Issue 1
The odd-eyed white cat if a phenomenon, both beautiful to see and interesting to study from a genetic point of view. For such a study, the breeder must consider not only the ways in which a white coat is inherited, but he must also learn something about the anatomy of the eye. The majority of cats have yellow or yellow-green eye color; and those that do not, have experienced some change in color physiology which has altered coat color and incidentally, eye color. In other words, the mutation which has changed coat color affects the cat as a whole, and eye pigmentation is included in the alteration. Among the genes and groups of genes affecting color are dominant white and piebald spotting. The usual yellow or intense copper eye color of cats results from the action of polygenes and is relatively free form the effects of coat color.
The odd-eyed white presents certain variances form normal pigment deposition in the eye itself. Eye pigment is found on the anterior and posterior surfaces of the iris. The presence of pigment on the front and back of the iris, in the choroid and retina, represents the normal situation. However, the bilateral blue-eyed white cat has pigment only on the posterior or back surface of the iris, and the quantity of pigment is reduced. Although the bilateral copper-eyed white has pigment on both surfaces of the iris, the amount is also reduced from the normal. These differences in amount and location hold true for the odd eyed white cat with regard to each eye.
From the discussion of eye color it is apparent that dominant white and piebald spotting alter color physiology. Therefore, there are at least two ways in which a cat may inherit a white coat. In addition, the genes for recessive white can produce an identical coat. It is easier for the breeder to understand the genetics of the odd-eyed white if he knows something about bilateral blue-eyed and bilateral copper-eyed cats.
The basic pigment eumelanin which is black in color is produced by the melanocyte, but in specific tissue environments phaeomelanin or red pigment is produced. The pigment cells are derived from neural crest material in the embryo and wander to places in the hair bulbs and are responsible for coat color. Melanocytes in dominant white, recessive white and in the extreme degree of piebald spotting do not function. They do not produce melanin. Melanocytes carrying pigment to the eye are derived in the optic cup; they are not affected by any neural crest abnormality, and therefore, the eye is colored although melanocytes do not function elsewhere.
Cells of the neural crest also differentiate into certain spinal ganglia, and strictures essential for hearing form from these nerve fibers. Therefore, an abnormality in the neural crest can ultimately result in deafness. The association of deafness in the blue-eyed white cat is, then, not coincidence. Deafness frequently occurs on the side of the blue eye in the odd-eyed white.
Robinson states that the white coat regardless of eye color or eye color symmetry is due to dominant white. Whiting states that the blue-eyed white cat occurs as a result of dominant white together with piebald spotting. Thus, the question of white coat in inheritance is unsettled.
Let us examine some facts and try to correlate a logical, although not necessarily true, answer.
1. Piebald spotting is caused by a number of genes. Their affects produce a cat which is basically white with colored spots. Therefore, these genes must interfere with function and/or migration of melanocytes. The extremes of piebald range from the solid-colored cat to the white cat with perhaps only a few, if any, colored hairs.
2. Abnormal neural crest material in the embryo results in nonfunctioning melanocytes and can also result in deformed or absent structures essential for hearing.
3. Melanocytes bearing pigmeat to the iris come from within the embryonic eye rather than the neural crest. Therefore, the iris can be colored although malanocytes do not function elsewhere.
4. Certain genes including dominant white and piebald spotting cause changes in coat color and in addition, alter eye color from the usual yellow or yellow-green.
What then are the genetic possibilities to explain the white coat, deafness, and variable eye color?
If dominant white and piebald spotting can each independently alter color physiology then the blue-eyed white may be homozygous, dominant white (W/W) or it may be due to the combination of piebald spotting and dominant white. (W/ss). If piebald spitting interferes with melanocyte migration and neural crest cells, then the deaf, blue-eyed white cat should be (W/ss). Since the copper-eyed white has normal eye color which has been intensified under the action of another group of genes, then the copper-eyed white is recessive white 9w/w0. This does not explain the decrease of pigment deposition in the copper-eyed white. The odd eyed white should be a combination of piebald spitting and recessive white.
Since so many variables are involved, it is difficult to predict the outcome of “white” breeding with any degree of accuracy, that is, in regard to eye color. Persian breeders through years of work have “set” white so that it dominates, without necessarily being “dominant white” (W/W). Breedings between a white Persian and a blue one will result in white kittens. Such a breeding in shorthairs would produce mainly, if not all, blue kittens.
Eye color, not being directly inherited, is most difficult to predict. Through intensive breeding the number of variables is decreased, and the breeder will learn from experience what his cats will produce. This can occur without specific knowledge of the genotype (genetic constitution) of his cats. Blue-eyed white bred to blue-eyed white will produce blue-eyed white, but deafness will become a serious problem,.
Blue-eyed whites bred to copper-eyed whites will involve the assortment of dominant white, recessive white and piebald spotting. It is interesting that there will be a tendency to a greater number of copper-eyed kittens, the eye color associated with recessive white. Blue-eyed and odd-eyed kittens will also occur. Blue-eyed whites bred to odd-eyed whites will produce blue-eyed, odd-eyed and copper-eyed kittens. The blue-eyed kittens will tend to be in greater number.
Since the inheritance of white coats is unsettled and because so little is known about the genetics of eye color, the breeder of odd-eyed whites is offered a challenging problem. What he learns will depend upon the accuracy and depth of his records and observations.
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White Cats: Odd-Eyed and Otherwise, Cat Fancy vol. 1 no. 1