Accuracy Angora Cat of color classification is essential for a study such as this. Most of the color classes of goats and kids were unmistakable, so that misclassification of kids was unlikely. Badgerface goats and black and tan goats, for example, are very distinctive throughout life and are unmistakable. Black goats, likewise, are easily identifiable throughout life.
Angora few color classes are more equivocal. Brown, for example, includes any kid born a reasonably brown shade. It is likely that brown therefore includes both eumelanic and pheomelanic types. A further difficulty with Angora goats is that both eumelanin and pheomelanin fade, although pheomelanin generally fades more than eumelanin. Regardless of this, it is likely that the brown classification represents more than one pigment type, and therefore it is of limited use in analysis. The only exceptions are goats that are of intermediate Agouti patterns, for which observers can be confident that the brown .regions are eumelanic. Similar arguments hold for the grey goats, since this color class includes any goat born with a mixture of eumelanic and pale fiber. These goats may arise from the grey allele at the Agouti locus, or could also be roan and the result of various white spotting phenomena. As such, the grey category was of limited usefulness for analysis. Fortunately both brown and grey goats were rare in these data.
Peacock was chosen to designate a pattern that is pheomelanic on the front, and has a eumelanic rear, lower legs and distinct eumelanic facial pattern. Peacock is the name given a goat breed that is consistently this pattern, and this name therefore helps to avoid some of the confusion that arises from trying to remember on mantled, reverse mantled, posterior mantle or anterior mantle whether the mantle is eumelanic or pheomelanic. The san clemente pattern, which is nearly the reverse of the peacock pattern, is also a useful designation since it is nearly uniform for the San Clemente Island goat breed. The use of these names is an arbitrary decision, but those familiar with breed characteristics will find it a precise way to describe these two distinctive patterns.
Red goats varied from being richly pheomelanic to being very nearly white. Such goats are unmistakable with other color classes, with the exception that very dark ones can be confused with brown goats. Red goats are usually born a fairly rich color, and then fade to a pale color. In most goats a portion of the primary fibers remain pigmented with pheomelanin, so that it is possible to identify red goats throughout life, even after they have faded. Some pheomelanic Angora goats have a variable shade of red with annual seasons, and so fade and then darken the color repeatedly.
White goats are starkly white with no pigmented fibers. This is the usual phenotype for Angora goats. White can result from a variety of biological mechanisms, including removal of pigment by white spotting, or removal by dilution. As a result, white as a color class can include a variety of genetic mechanisms all leading to a single endpoint.
The color, and the whiteness, of sheep is relatively better studied than that of goats. Whiteness of sheep generally results from the white or tan allele!. In many breeds of sheep various spotting phenomena are also involved in producing starkly white sheep. Spotting combines with the white or tan allele to result in sheep that are more extremely white than those with the white or tan allele but lacking spotting patterns. In addition, selection for extreme degrees of spotting can result in starkly white sheep that have Agouti phenotypes other than white or tan. Some spotting phenomena in sheep, specifically Akaraman type spotting, consistently result in fleeced regions that are white, with minor pigment remaining only in nonfleeced regions!. White spotting mechanisms are useful for producing starkly white fleece, since pigment cells and therefore pigments are entirely lacking. Spotting mechanisms on their own appear to have been used relatively rarely in white sheep breeding, which relies mainly on the white or tan allele at the Agouti locus for the production of white phenotypes.
Of critical importance to this study is documentation that a single allele, white or tan at the Agouti locus, can be responsible for phenotypes that range from dark tan to white. The results from the Tennessee goat crosses demonstrate that the white or tan allele can indeed cause these variable phenotypes. The tan buck is heterozygous for white or tan and nonagouti, as demonstrated by producing black kids from mates with intermediate Agouti alleles, as well as kids with maternal Agouti intermediate patterns which are obligate heterozygotes for his nonagouti allele.
All but two does to which he was mated had previously been proven by production or pedigree to be heterozygous (or in some cases homozygous) for nonagouti. The data include two tan does, one of which was heterozygous for black and tan, and the other of which is heterozygous for badgerface. The kids from these two must be removed from the data since it is uncertain if they have received the white or tan allele from sire or dam. By removing the kids from these two tan does it is assured that all kids that are black or some intermediate Agouti locus pattern have received the nonagouti allele from the sire, while all tan or white kids (if these are due to a single allele) have obtained the white or tan allele from this buck. When the kids are so grouped, the result is that he passed to the kids eight nonagouti alleles, and ten white or tan alleles (P = 0.167 by binomial expansion).
If the white kids are not the result of the same Agouti allele as the tan kids, then these should be due to a locus other than Agouti and can be removed from the analysis. The result should still be that half of the nonwhite kids are tan and half are nontan. By doing this, the results are eight kids bearing the buck’s nonagouti allele, and only three bearing his white or tan allele (P = 0.08 by binomial expansion). This result is therefore unlikely, although not significant. It does remain most likely that the white or tan allele accounts for both the tan and the white phenotypes in this kid group, perhaps as determined by modifiers at other loci. The importance of this result lies in the fact that the white or tan allele can account for white as well as intensely pigmented pheomelanic goats. White can, therefore, segregate (with tan) as if at the Agouti locus, as determined by a previous study (2!. This previous studies did not directly document the range of phenotypes arising from a single allele originating in a single animal.
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