Fancy rats, or domestic rats, belong to the same species as the wild brown rat (Rattus norvegicus), much like domestic dogs belong to the same species as the gray wolf. Many varieties of fancy rats exist, among them hairless rats and double rex rats. Though the hairless rat and double rex bare some similarities, a number of differences exist between them, including certain biological functions.
Type of Rat
Hairless rats constitute a type of fancy rat. The double rex rat, on the other hand, is one of three types of patchwork hairless rats. While the hairless rat constitutes its own variety of fancy rat, the double rex is a type of an overall variety, meaning that the double rex is a specific type of rate, while a hairless is one of a number of types.
Fur or Lack Thereof
As the name implies, hairless rats have no fur, though they may have fuzz on their ankles, face and pubic areas. Patchwork hairless rats such as the hairless rex have fur in patches. Some portions of the double rex bear fur and some portions appear hairless. Double rex fur patterns are random. Hairless rats lack whiskers in addition to being furless. Their skin appears translucent on account of a lack of fur. Double rex rats generally have whiskers, though their whiskers sometimes appear rigid and curled, lacking the length and elasticity of standard rat whiskers.
True hairless rats, or those with 100 percent hairless genes, lack a thymus, an integral part of the rat immune system. This makes hairless rats susceptible to allergies and a number of health problems, such as tumors, eye and respiratory infections, heart or kidney disease, diabetes or skin problems. Hairless rats from mixed hairless/furry parents do have a thymus. Not having a thymus shortens the lifespan of the rat; hairless rats commonly live nine to 18 months. Double rex rats have a fully operation thymus and live a standard rat lifespan of two to three years.
True hairless rat females do not lactate enough to support a litter and resort to cannibalism or abandonment. A furry female rat carrying the hairless gene may produce both hairless and standard offspring. Rat Chatter recommends breeding hairless rats with a hairless father and furry, hairless gene-carrying mother to ensure healthy offspring. Double rex rats are the offspring of two rex parents, as the name implies. Rex rats have thick, long, curly fur. In order to produce patchwork hairless double rex offspring, both parents must carry the patchwork hairless gene.
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