 Hairless rats are a coat variety characterized by varying levels of hair loss . Hairless rats , bred from curly @-@ coated rexes , range from having areas of very short fur to being completely bare . Hairless rats are genetically produced by breeding different combinations of the genes that cause Rex coats . Since rex is a dominant trait , there only needs to be one rex parent to produce curly rex @-@ coated offspring . However , when two copies of the trait are present , by breeding two rexes together , the coat is affected differently — causing hairlessness , and earning the colloquial name , " double @-@ rex " . One subset of semi @-@ hairless rats , Patchwork rats , constantly lose hair and regrow it in different " patches " several times throughout their life . 
