Congenital / Hereditary Alopecia Figure 2

Figure 2: Basic types of genetic alopecia

Interesting fact:

Hairless rats have higher oxygen consumption and higher basal metabolic rates than haired rats.

Double Rex

Double rex is 2 doses of the dominate rexing genes (re, cu-1, or Cu-2) A double rex will exhibit very limited hair/fuzz or sparse hair particularly on the head, the hind end, and the legs. At times it will somewhat come and go. Patchwork Hairless is also a double dose of the rexing genes. They will have patches of short fuzz that can come and go and often appear over different parts of the rat’s body.


There are various true types of genes that cause hairlessness in rats. Some are associated with certain health/breeding issues. Many lines in the pet rat breeding community have overcome these issues. The hairless genes are recessive and will produce hairless rats when bred only with another hairless/or carrier.

The Genes that give us Genetic Alopecia

Mock Hairless/Double rexed/Patchwork Hairless
(Often sparse hair on head and posterior that will come and go)


The gene Re – Rexing locus (dominant)

Re/Re = rexed or mock hairless

Re/re = rexed coat

re/re = standard coat

Cu1 & Cu2

The gene Cu – Curly Locus (dominant)

Cu/Cu = curly or patchwork hairless

Cu/cu = curly

cu/cu = standard coat

True Type Hairless

Hairless rats

(predicted-chromosome 15)

(Only showing *at most* curly whiskers. This type has been reported to have some lactation problems.)

The gene Hr – Hair locus (recessive)

Hr/Hr = standard coat

Hr/hr = hairless carrier

hr/hr = Hairless

Shorn Rats

(chromosome 7)

(A spontaneous lab mutation discovered in 1994 at the lab in CCSU (Central Connecticut State University , — Archived page from 2008-07-06 (via the Wayback Machine)). Shorn rats are hairless These rats have abnormal hearts and kidneys which result in a short life span and don’t tend to live as long as other rats. The life expectancy is only 12-14 months of age.)

The gene shn – Nude Locus (recessive)

Shn/Shn = standard coat

Shn/shn = shorn carrier

shn/shn = shorn hairless

Fuzzy Hairless

(chromosome 1)

The gene Fz – Fuzzy locus (recessive)

Fz/Fz = standard coat

Fz/fz = fuzzy carrier

fz/fz = fuzzy hairless

Rowlette Nude

(Chromosome 10) AKA- rat athymic nude or Winged-helix nude (Whn) (Hairless with lowered immune function due to the lack of a thymus gland can carry viral infections sub clinically)

The gene Rnu- recessive

Rnu/Rnu = standard coat

Rnu/rnu = rowlette nude carrier

rnu/rnu = rowlette nude hairless

Frizzy Hairless

(predicted chromosome 1)

(Mutation developed by Charles Rivers Labs)

The gene Fr- recessive

Fr/Fr = standard coat

Fr/fr = frizzy carrier

fr/fr = frizzy hairless

  • Ahearn, K., Akkouris, G., Berry, P., Chrissluis, R., Crooks, I., Dull, A., Grable, S., Jeruzal, J., Lanza, J., Lavoie, C., Maloney, R., Pitruzzello, M., Sharma, R., Stoklasek, T., Tweeddale, J., King T. (2002). The Charles River “hairless” rat mutation maps to chromosome 1: allelic with fuzzy and a likely orthologue of mouse frizzy. J Hered, 93(3), 210-3. Retrieved December 24, 2008, from the Medline database.
  • Boardman, B., & Boardman, L. (n.d.). Rat Genetic Code Basic Explanation. Retrieved December 24, 2008, from
  • Genetics Tutorial. (n.d.). Retrieved December 24, 2008, from
  • The Rat Genome Database. (n.d.). Retrieved December 24, 2008, from

Genetic Resource courtesy of Bellaratta’s Nest Rattery


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