By Nanna M. Andersen | Published: 19.11.21 | Edited: 02.07.23 I want to discuss three papers: two of them about the variety called Fawn, genotype ff (not to be confused with the Fawn, A* rr, which is an Agouti-based rat with Red Eye Dilution). They are not the same gene. Additionally, I will review a paper about a fancy-derived Mink mutation. Fanciers believe that UK Mink may be a recurrence of Fawn (ff). The discovery of Fawn (ff) occurred in 1945 in a line of Blue rats, as described in "Linkage of the Norway Rat VIII" by Dr. King. This new mutation was described as "coffee brown", suggesting it was a rather dark brown. In 1949, it was established that Fawn is linked to Agouti, as explained in the paper "Linkage of the Norway Rat X" by Dr. King. Agouti is found on chromosome 3 (GenBank accession No. NC 005102), so we can conclude that Fawn (ff) is also located on chromosome 3 seeing they are confirmed linked. Regarding genetics theories, the colorized picture displays the Fawn's color (seen second from the left). The lineup, from left to right, includes Black, Fawn, Russian Blue, and Russian Dove. Which in the study is mentioned as: Black, Fawn, Blue and Lavender. Although the color is an approximation due to the original picture being black and white, it is clear that Fawn is rather dark and could almost resemble a Chocolate. Based on the limited descriptive words about this Fawn mutation, it seems that the Fawn mutation is what we know in the fancy rat community as UK Mink (mm). in 1994 a Mink variation emerges in the scientific community and R. Robinson received the rats from fanciers. These rats were called Mink and Pearl, respectively. Robinson wrote the paper "Mink and Pearl: New Color Mutants in the Norway Rat". At that time, the scientific community did not have a Mink variety, and this "new mutation" was named Mink and designated the genotype "mm". There were distinct differences observed when comparing this new Mink to the Fawn described by Dr. King in 1945. These differences are significant when comparing them to the two Mink varieties we have in the fancy rat community. The new Mink studied by Robinson was not described as "coffee brown" but rather as "light brown," resembling "milk chocolate, cafe au lait." This description does not match the picture from the 1945 study. Furthermore, the eyes of this new Mink mutation were described as sometimes having dark-ruby colored pupils, as well as a light or even white undercoat. These characteristics suggest that this new Mink may actually be Mock Mink (also known as American Mink) and not UK Mink. Robinson even mentioned in the end of the paragraph that this new Mink is not a repeat of the Fawn mutant. In the study this new Mink were crossed with Chocolate (bb) to determine if the genes were allelic (on the same locus), but it was discovered that they were not. However, it was noted that the "aa bb mm" genotype produced a color similar to that of "aa mm", and it was challenging to distinguish between the two. This led to speculation that this new Mink is epistatic to Chocolate, meaning that when the "mm" genotype is present, it does not allow the Chocolate genotype to be expressed. The Mock Mink (American Mink) gene have been mapped to Chromosome 1 (Genetic Analyses of Fancy Rat-Derived Mutations), which definitively rules out Am Mink being a recurrence of Fawn, as Fawn is located on Chromosome 3. References
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