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Oh-Naturel Sphynx Cattery

Genetics

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The SPHYNX, above all else, is a hairless cat. The hairlessness of the SPHYNX, of course, results from differences in hair deposition and/or maintenance between the SPHYNX and normally coated breeds. We will discuss empiric, scientific and statistical data as it relates to the physiologic, biochemical and genetic differences that separate the SPHYNX from other normally coated breeds and that allow for variances within the SPHYNX for degree of hairlessness. Sanspelo suggests that you review the discussion on normal feline hair growth before reviewing the discussion of hairlessness.

The history of hairless cats--note that "hairless" is a relative term in this discussion as most hairless cats do have at least a fine stubble of hair--is a repetitious cycle of the spontaneous, sporadic appearance of one or two hairless cats in a litter with other normal coated siblings. As we move through the twentieth century, we see that those naturally occurring mutations are reported approximately once a year somewhere in the world--usually in the northern latitudes of North America or Europe. In our development of the SPHYNX breed, we have worked with a particular gene for hairlessness (hr) which we describe in Mendelian genetic terms as recessive to the gene for normal coat (Hr) and incompletely dominant to the gene for the Devon Rex coat (re). However, in observing our SPHYNX through their life cycles, we note that some SPHYNX known to be heterozygous with the Devon gene (hr re) remain very hairless throughout all conditions of their entire lives, some relatively hairy throughout all conditions of their lives and some vary depending on their environmental and hormonal conditions. Likewise, SPHYNX known to be homozygous (hr hr) also fall into a similar spectrum. Further, we know that this gene site (hr, Hr, re) can determine hair stability (SPHYNX ) and/or curliness (Devon Rex) and that hairs that do grow carry the pigment of their coat color at the site of deposition--this categorizes them as either primary or secondary guard hairs and suggests the lack of Down hairs in the SPHYNX . Lastly, we have observed that the SPHYNX phenotype is associated with a decreased anagen:telogen ratio, early breakage of the cat's whiskers and early loss of teeth, which are similar to hair in that they are also of ectodermal origin thus giving them a commom developmental pathway.
If we can't predict absolute hairlessness with these genes and observations, what can we predict? We can say that SPHYNX generally have less hair than cats with normal coats--usually much less! We can also say that SPNHYX generally have a coat thickness that varies with environmental and hormonal conditions--some SPHYNX more than others--as do cats with normal coats. Therefore, we can conclude that hairlessness in our SPHYNX depends on at least two gene systems: one at a single genetic locus which influences the primary Guard hairs' straightness, thickness, stability and the other with multiple determinants influencing location and situational variance of the secondary Guard hairs (Awn hairs) with respect to environmental and hormonal stimuli. Author Sanseplo