Did you know that the AGA has a long history of publishing about cats? Not just the beloved felines that have commandeered many homes and communities (not to mention ecologically devastating many areas…), but also their wild brethren. In fact, Darwin even mentioned cats in his Origin of Species, where he discussed the relationships between both blue eyes and deafness as well as calico coloration and sex. In the next few blog posts I am going to describe some of the work published about our feline friends in the Journal of Heredity. A reminder to all our members, you get free access to the articles mentioned from your membership homepage on the website!
This post features articles from the 1930s regarding Siamese coloration (and crosses) as well as the event of a two-faced kitten. Our next post also features articles from the 1930s, but features a saga of hairless cats, from the birth of one named Nonesuch to her first litter of kittens…
TEMPERATURE EFFECTS ON THE COLOR OF THE SIAMESE CAT
As an American PBS kid, I watched episodes of Sagwa the Chinese Siamese Cat (based on the book by Amy Tan), which helped cement my love of both public broadcasting and cats. Little did I know at the time that the characteristic cream coat with dark points of the Siamese cat were due to the effects of a temperature-sensitive enzyme. Prior to the 1930s, researchers had shown that the distinct coloration of Himalayan rabbits varied with temperature and was inherited as a recessive trait. It was thought that Siamese cats, known for their outgoing natures and lovely pointed coats, had a similar inheritance pattern and mechanism responsible for their coloration.
To determine if a similar mechanism was at play in Siamese cats, the authors subjected a pair of cats to lower temperatures during their shedding period. Lo and behold, the creamy base coat of the kitties gradually darkened to a browner color closer to the original color of their points. To then see if this color change was reversible, the authors then shaved the area on the cats over the shoulders and back and put them in cute little vests (see the photo on the right) to locally warm that area. They then discovered that indeed the coat under the treated area lightened back up. Thus it was determined that the Siamese cat was a true example of acromelanism.
Where do I sign up for experiments involving putting pets in sweaters?
A Two-faced Kitten
Here we have a report of (including a photo, check out the article if you want to see it) craniofacial duplication in a kitten. At this point this is generally accepted to be caused by an over-expression of Sonic hedgehog (SHH) during development that is observed across vertebrates. Sadly, the kitten did not live very long.
ALLELOMORPHISM OF SILVER AND SIAMESE COAT VARIATIONS IN THE DOMESTIC CAT
In this article, Keeler and Cobb explore the genetic underpinnings of the so-called chinchilla (below, B)/silver (below, F) and Himalayan (below, A)/Siamese (below, H) coat dilutions. The chinchilla/silver color is characterized by the loss of any yellow pigmentation (i.e. pheomelanin) to the coat but relatively normal black pigment (ie eumelanin). In the rabbit, both mutations are recessive traits, but when Himalayan and chinchillas are crossed the hybrids retain both parental phenotypes, leading researchers to the hypothesis that they are allele of the same gene.
In cats, Siamese coloration is recessive to ‘normal’ pigmentation, as shown by crosses by the authors between Siamese and Persian cats, which resulted in all black kittens (above, J) and from records by a Miss Doris Bryant. The authors also determined that the silver gene must also have a recessive inheritance, due to crosses in Persian cats (above, F as a regular silver tabby and G as a silver non-tabby “smoke”).
I would also like to take a moment to acknowledge that the three cats on the righthand side are indeed Persians, which nowadays are known for their extreme brachiocephalic look (aka having a smushed face). It’s amazing to me what artificial selection has created in less than 100 years. Persians used to be fluffy but have relatively normal (and functional!) snouts, but now are plagued by breathing issues due to having their nasal passages aggressively shortened to achieve their distinct look. At least they are still fluffy, I guess?
ANYWAYS. The authors then crossed a silver tabby Persian male with a Siamese female and got a litter of silver tabbies (above, I). They also crossed a Siamese female with a “smoke” Persian male and had a corresponding litter of all smoke kittens. Thus, the authors concluded that silver and Siamese are also alleles in cats like they are in rabbits!
Siamese-Persian Cats
The same authors from above, probably on their quest to uncover the genetics of silver/Siamese, stumbled upon something else entirely: the origin of the Himalayan Persian! They employed the time-tested method of backcrosses (gotta love some inbreeding in the name of trait-fixing, see below) to combine Persian traits (long hair) with the Siamese coloration. Huzzah!
This brings us to the end of the first part of the 1930s. Our next post will feature some really fun, really naked cats (aka the Sphynx mutation)!
About the Author
Miranda Wade
received her B.S. in Biological Science from Colorado State University and her dual PhD in Integrative Biology and Ecology, Evolutionary Biology, and Behavior from Michigan State University. During her time in the Meek Lab at MSU, her work consisted of using ‘omics to address various conservation questions about land-use change and microplastics exposure. She is currently the Social Media Editor for the American Genetic Association and a PostDoc in the Sin Lab at the University of Hong Kong. For her postdoctoral work, she is exploring the genomic basis of coloration in birds. She is the proud owner/caretaker of three cats.