Stirrin' Up The Gene Pool

By Barbara Redalia

Have you ever considered breeding cats of a new or unusual color or pattern? Been interested in people’s lyrical descriptions of chocolate and lilac smokes, tabbies, silvers and bicolors but not known enough about how to produce them? Follow along some examples while we outline breeding plans capable of producing these (and other) colors, starting with crosses of (a) chocolate point by silver, (b) chocolate point by brown (genetically black) tabby, (c) chocolate color point carrier (CPC) by blue smoke lynx point, and (d) chocolate CPC by blue and white bicolor.

To begin with, since none of these colors are sex-linked it makes no difference which parent is male and which is female. Small letters designate recessive genes; capital letters signify dominant genes.

A. Chocolate point by silver mating

The genotype of these parents may be designated thus:

In this example it is assumed that neither parent carries the “d” gene for dilute color; thus none of the offspring of this mating can be dilute. In order to produce a dilute kitten (blue or lilac) both
parents must have at least one dilute gene. If the chocolate point parent has thrown any dilute kittens or has a dilute parent it must carry the dilute gene. Because most silvers are ‘color bred’ the silver is unlikely to carry the dilute gene; hence even if the chocolate point is heterozygous (Dd) the homozygous (DD) of the silver would assure that all kittens would be (D-) dense. Under the above assumptions all the offspring of the above breeding will have the genotype Aa Bb Cc DD Ii and their phenotype (appearance) will be as follows (taken gene by gene):

Aa - stripes
Bb - black pigment
Cc - full coat color
DD - dense color
Ii - tipped coats

They would be described as silver tabbies; eye color is usually hazel. This first generation can be pretty boring to those who like to see color variation in kittens, but when two cats of this genotype are bred to one another there are more possibilities:

Probable offspring from crossing of two heterozygous silver tabbies:

Genotype Phenotype Summary

Because there is no linking among the above characteristics there is no way to control whether a chocolate kitten resulting from the above breeding would also have (a) a tipped coat, (b) the Siamese coat pattern, or (c) tabby stripes. If we wish to know the genotype of the chocolate kitten, the chocolate kitten is most likely (75%) to have a tipped coat and (75%) stripes, i.e. to be a chocolate tabby smoke, or it could instead be a chocolate point (bb cc), a chocolate lynx point(A- bb cc), a chocolate smoke lynx point (A- bb cc I-), a solid chocolate (aa bb C- ii), or a chocolate smoke (aa bb C- I-).

B. Chocolate point by brown tabby

One sometimes hears people recommending that one cross chocolates with brown tabbies to achieve other colors of chocolates. One might capitalize on the nice type of the brown tabbies by so doing, but, because the brown tabby does not have the inhibitor gene (I-) which causes tipping and removes the gold band there would be no smoke or “tipped” cats resulting from such a cross. Otherwise the results would be similar to the results from crossing a chocolate point with a silver, except that the yellow agouti banding would remain, producing golden tabbies rather than the tipped coat of the silver tabbies. Chocolate goldens could then be produced by breeding these golden tabbies which carry the chocolate gene to solid chocolates.

C. Chocolate CPC (dilute carrier) by blue smoke lynx point (chocolate carrier)

If one wishes to produce varieties of lilac kittens as well as chocolates it is necessary to have at least one dilute gene in each parent. The cats described above have the following genotypes:

aa bb Cc Dd ii X Aa Bb cc dd Ii

2/ 4 Aa Agouti (stripes)
2/4 aa Non-agouti (no stripes)
2/4 Bb Black pigment
2/4 bb Brown pigment (chocolate)
2/4 Cc full coat color
2/4 cc Siamese coat pattern
2/4 Dd Dense pigment (black or seal pt.)
2/4 dd Dilute pigment (blue or lilac)
2/4 Ii Inhibitor gene - tipped coat
2/4 ii non-tipped coat

Note that for each gene we are combining a homozygous recessive (e.g. aa) with a heterozygote (e.g. Aa) with the result that in the offspring the probability is for 50% expression of each allele. There is no linking among the above characteristics, that is, they are inherited independently of one another. From such a breeding, over the long haul, one would expect equal numbers of striped vs. non-striped, black vs. chocolate pigment, full coat pattern vs. Siamese coat pattern, dense vs. dilute colors, and tipped vs. non-tipped coats. Also, clearly if one is interested in kittens of a lilac color (bb dd) there must be chocolate (b) and dilute genes (d) in both parents.

D. To produce chocolate bicolors is relatively straight-forward. Here we have added the ( S) symbol to represent the white spotting gene, which is dominant. and also additive, so that the cat which is SS tends to have much more white than the cat which is Ss. One could combine a chocolate CPC (which carries dilute) with a blue and white bi-color. This cross is represented as follows:

( bb Cc Dd ss X BB CC dd Ss)

The first generation cross between these two cats results in cats of these genotypes:

4/4 Bb black pigment (chocolate carriers)
2/4 Cc full coat color (heterozygous)
2/4 CC full coat color (homozygous)
2/4 Dd dense coat color (heterozygous)
2/4 dd dilute coat color (blue)
2/4 Ss with white spotting
2/4 ss no spotting

The probability is for equal numbers of black and blue, spotted and unspotted cats, and no Himalayans, since only one of the parents carried the recessive (c) gene. Once again we need to go to the second generation to see cats of the desired chocolate and lilac colors. The first cross between the chocolate CPC and the blue and white bicolor yields the following genetic probabilities:

4/4 Bb All have black pigment (chocolate carriers)
2/4 CC; 2/4 Cc Half carry the Siamese coat pattern gene (c)
2/4 Dd; 2/4 dd Half black, (dilute carriers), half blue (dd)
2/4 Ss; 2/4 ss Half with white spotting, half with none (S)

Since we are aiming at chocolate and lilac bicolors we would select to breed those with white spotting. Those without white spots do not carry the spotting gene, since (S) is dominant it shows. We do not know without test-breeding which of these cats carries the Siamese gene (not desirable in bicolors). Since all of these cats have the chocolate gene, however, they are potentially useful in breeding other varieties of chocolates if their type is good. If we are particularly interested in lilac bicolors we would want to select at least one dilute from this breeding rather than black, to increase the probability of lilacs. Suppose we select to breed together a black and white bicolor and a blue and white bicolor from the above breeding. One happens to carry (c), the Siamese gene, and both carry chocolate:

Bb Cc Dd Ss X Bb CC dd Ss

The probabilities for their offspring would be as follows:

1/4 BB black pigment 3/4 will have black pigment
2/4 Bb black (chocolate carrier)
1/4 bb chocolate 1/4 will be chocolate
2/4 CC full coat color (homozygous) all will have full coat color
2/4 Cc full coat color (colorpoint carriers)
2/4 Dd dense 2/4 will be black or chocolate
2/4 dd dilute 2/4 will be blue or lilac
1/4 SS homozygous for white spotting 1/4 (probable van)
2/4 Ss heterozygous for white spotting 2/4 bicolors
1/4 ss no white spots 1/4 no white spotting

One might wish to breed one of the cats of the above breeding to a visible chocolate or lilac (bb), since that would double the probability of obtaining chocolate or lilac kittens:

bb Cc Dd Ss X Bb CC dd Ss
2/4 Bb black 2/4 black (chocolate carriers)
2/4 bb chocolate 2/4 will be chocolate or lilac
2/4 CC full coat color (homozygous) all will have full coat color
2/4 Cc full coat color (colorpoint carriers)
2/4 Dd dense 2/4 will be black or chocolate
2/4 dd dilute 2/4 will be blue or lilac
1/4 SS homozygous for white spotting 1/4 (probable van)
2/4 Ss heterozygous for white spotting 2/4 bicolors
1/4 ss no white spots 1/4 no white spotting

This should keep us busy for a few years!

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