Rex mutations
And now for my favorite mutation of all...the rexing genes!! Rex mutations basically slow the growth of a rat's hair in the anagen phase of growth, mainly in the guard hairs, so the hairs are shorter, thinner, and not perfectly formed, resulting in the curly appearance of the rex rat! Currently, there are two different genes that are known to cause the rex mutation. The first is very rare in the fancy rat community and pet trade, but will still be noted here. It has been hypothesized that the wavy mutation still exists, but exists in the same lines as those with the rex mutation, creating a 'rex' rat that also has the recessive wavy alleles. In these rats, the fur is quite sparse, and is more like a downy, thin covering on the body. It is distinct from both the other mutations as they occur independently. I will also make mention of a couple others in the end, there are now assumed extinct mutations. The fertility and survival rates of curly haired rats is normal.
Wavy mutation (wv) - recessive
Wavy rats look just like rex rats, but the hair is a bit thinner and shorter. Their whiskers are curly and bent. The significance of this mutation is that it is recessive, unlike its rex counterpart.
Rex mutation (Re) - semi-dominant
Rex rats are a passion for me, and I personally breed them. The coat of a rex rats can vary quite a bit, but in general, they are wooly looking. The coat goes through a series of changes, starting soft and fluffy in weaning rats to a rougher texture through early molts. The hair is usually of normal thickness, but because of the curly nature of the hair, you can often see the skin underneath. Because the rex mutation is semi-dominant, when two copies are present, another look all together is produced. This is often referred to as the double-rex. Around 4 weeks of age, a double-rex rat will begin to rapidly lose it's coat, starting at the head and shoulders and moving down the body in the normal pattern of hair growth/cessation of growth. A new coat will come out and that new coat will also be lost as the rat molts. This may occur over the rat's entire adult life. Males are less affected than females, and tend to retain a bit more hair over all. The hair of a double rex rat is also easy to pluck out, and the whiskers are shorter than that of a rex.
Other mutions causing the rex appearance...
Curly-1 (Cu-1) is a dominant trait resulting in a slightly wavy coat, that is usually relaxed by adulthood, but the coat remains softer than that of a rat with a standard coat.
Curly-2 (Cu-2) is a dominant trait resulting in a similar coat to Curly-1, but with a more distinct curl, but one that still relaxes a bit as the rat ages.
Kinky (k) is a recessive trait on Chromosome 4. Adult coats on this rat are shorter, rougher, and more dense. And, due to easy breakage of the hair, bare patches develop in areas like the shoulders and hips. These rats have a lower fertility and shorter lifespan than other rats.
Shaggy (Sh) is a dominant trait on Chromosome 2. This mutation gives an appearance somewhere between the two Curly mutations, and there is some interaction with this gene and the others, because when both are present, the curling of the hairs is more significant.
Other terms heard in the rat fancy include 'teddy rex' and 'velveteen', but these are more or less cute names for variations of phenotype. Most likely, these are the same mutations that have been selectively bred for a certain rex type, but at this point, it is unclear. It is also possible, although less likely, that these are new mutations or re-occurances of the formally assumed extinct mutations.
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