This Web page, illustrating guinea pig genetics with pictures big enough to see what's going on, helps promote Knoxville Guinea Pig Rescue and your local guinea pig rescue operation. Don't breed guinea pigs or buy them from pet shops - rescue them! Most of the animals on this page will be rescues.


This family of Crested guinea pigs all express the dominant trait Star (St) - called "crested" by fanciers. Star suppresses the expression of the Rough (Abyssinian) gene, and should not be bred into Abyssinian or Peruvian stocks.
The baby in the middle is a self tortoise shell and white (aa B C e^pe ss) - the white spotting organizes the effect of the tortoise shell gene into large patches instead of an irregular roan-like pattern. The tortoise shell gene is not X-linked like it is in cats - there are both male and female tortoise-shell guinea pigs.

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This unusual animal is a dark-eyed (hard to see in the flash photograph) white boar named Herbie. Dark-eyed white animals are usually white spotted (ss) but have no colored patches - they're one big white spot. Dominant white genes probably exist in guinea pigs also.

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When I was a boy I bred Dutch-patterned red-eyed sepia-white agoutis (A B E c^rc^r ss) - this was New Guinea, in 1949.

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This oddly furred guinea pig is probably heterozygous for the long hair gene, and looks like he has a "rat" such as is worn by grade school boys. This is an unusual expression of the gene. This agouti animal has diluted dark melanin, probably because of the brown gene (A E bb C S) which does not lighten the red (yellow) color.

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This alert little dust mop is a Peruvian, with long hair (a recessive trait, with no gene symbol in common use) and has rosetted (rough, Abyssinian if he were a shorthair) hair (R). He has red (yellow) hair, with white Dutch spotting - (C ee ss). You cannot tell what his agouti or brown locus genes are.

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Reading notes for a bibliography of guinea pig genetics (cavy genetics).

The Biology of Hystricomorph Rodents. Proceedings of a Symposium, London, June 1973. I.W. Rowlands and Barbara J. Weir, eds. published for the Zoological Soc of London by Academic Press, NY 1975. Symposia of the Zoological Society of London, No. 34.
Reviewed in Science 29 Aug 1975;189:713-4.
"The final chapter, on the origin of the domestic guinea pig, by [Barbara J.] Weir, will be of interest to guinea pig enthusiasts, although it does not resolve the problem."

The guinea pig. Gale Cooper and Joseph Carlisi. Illustrated by Gale Cooper. Harvard Magazine, June 1976, page 44. [Scan this]

Brehms Tierleben, 1921. Bad photocopy. In Fraktur.

Guinea-pig and Cavy, entries in old OED.

Reprints of three papers by Barbara J. Weir, at the Wellcome Institute of Comparative Physiology, Zoological Society of London, Regent's Park, London NW1.

The Care and Management of Laboratory Hystrichomorph Rodents. Lab. Anim. 1967;1:95-104. 
Caging, feeding, and handling of Dasyprocta aguti (the agouti), Myoprocta pratti (acouchi), and Hystrix cristata (African porcupine). With B and W photos of each species.

The Care and Management of Some More Hystrichomorph Rodents. Lab. Anim. 1970;4:83-97. Cavia aperea and Galea musteloides (wild guinea pigs), Octodon degus (the degu), and Lagostomus maximus (plains viscacha). With B and W photos of each species.

Guinea Pig Estrus Cycle Behavior: Young WC, Dempsey EW, Myers HI. Cyclic Reproductive Behavior in the Female Guinea Pig. J. Comp Physiol 1935;19:313. The classic description of the estrous cycle.

Weaver, Kenneth F. The Five Worlds of Peru. National Geographic, February 1964, page 258. "In Cuzco's cathedral, a painting of the Last Supper by a Cuzqueño artist caught my eye with one incongruous detail; a while roasted guinea pig on platter before Christ and the apostles. the detail is not meaningless; for generation s the sierra Indians have considered guinea pig a delicacy. We tried it and found it much like rabbit."

Wright, Sewall. "Genic Interaction". In Methodology in Mammalian Genetics,  Burdette WJ, ed. Holden-Day, San Francisco 1963.

Wright, Sewall. "On the genetics of hair direction in the guinea pig. J Exper Zool 1949;112:303 and 325; also 1950;113:33. Star (crested)

Ibsen HL. J Hered 1951;42:267. Roan.

Papers and books by William Ernest Castle, professor of zoology at Harvard.

1. Heredity of Coat Characters in Guinea-Pigs and Rabbits. Carnegie Inst. of Wash., Pub. #23, Feb 1905. Papers of the station for Experimental Evolution at Cold Spring Harbor NY #1. Contributions from Zoological Library of the Museum of Comparative Zoology at Harvard. #158.

2. Heredity of Hair-Length in Guinea-Pigs and its Bearing on the Theory of Pure Gametes. (with Alexander Forbes). 

3. The Origin of a Polydactylous Race of Guinea-Pigs. Carnegie #49, May 1906. Cold Spring #5, MCX #175.

4. Studies of Inheritance in Guinea-Pigs and Rats (with Sewall Wright). Carnegie #241, Sept 20, 1916. Cold Spring #26. From the Laboratory of Genetics of the Bussey Institution.
Part I. An Expedition to the Home of the Guinea-Pig and Some Breeding Experiments with Material there Obtained. pp 1-58. (by WE Castle)
Part II. An Intensive Study of the Inheritance of Color and of Other Coat Characters in Guinea-Pigs, with Especial Reference to Graded Variation. By Sewall Wright. pp 59-121.
Part III. [about piebald rats] by SW.

5. Genetics and Eugenics, 2nd ed., Harvard 1920.

6. Mammalian Genetics, 1940. (I have never seen this book.)

YELLOW runs from red through yellow and cream to white.

BLACK dilutes from black through dull brown and tow-color to white. Castle called this color sepia, but the fancy called it blue. Castle noted in fact that a blue (like a blue rabbit) color existed in Cavia cutleri, fully interfertile with the domestic animal. 

BROWN dilutes from chocolate to white. the colors are "richer, warmer, less dull" than the sepias. 

Agouti nomenclature:
black-red = golden
sepia-yellow = yellow
sepia-cream = silver
brown-red = cinnamon
brown-cream = light cinnamon.
	
E and A type	E+A+	E+aa	ee any A,a
BPC	BRA	B	R
BPCdCd	DSYA	DS	Y
BPCdCr	DSCA	DS	C
BPCdCa	LSCA	LS	C
BPCrCr	DSWA	DS	W (LP)
BPCrCa	LSWA	LS	W (LP)
BPCaCa	W (DP)	W (DP)	W (LP)

BppC	pale SRA	pale S	R
BppCdCd	v pale SYA	v pale S
BppCdCr	v pale SCA	v pale S
BppCdCa	v pale SCA	v pale S
BppCrCr	v pale SW A	v pale S
BppCrCa	v pale SW A	v pale S
BppCaCa	W (LP)	W (LP)

bbPC	bRA	b	R
bbPCdCd	MbYA	Mb	Y
bbPCaCr	MbCA	Mb	C
bbPCdCa	LbCA	Lb	C
bbPCrCr	MbWA	Mb	W
bbPCrCa	LbWA	Lb	W
bbPCaCa	W (LbP)	W (LbP)	W

bbpp [lilac series] hadn't been tried.

Rough (Abyssinian) fur - complex grading system, the lowest of which ("rough E) had hair growing the wrong way on the toes. This grading resulted from the action of a rough modifier gene, first called (confusingly) S, later M.

Wright S. Two New Color Factors in the Guinea Pig. American Naturalist 1923;57:42. The two new factors are Ck and F. CkCk homozygotes are hard to tell from C. But the yellow is diluted almost as much as by Cd. 
F is the "fader" gene - ff causes fading of YELLOW as animals age.
Cr may have been introduced by WE Castle form Peru in 1912. WEC got Ck from the Bureau of Animal Husbandry. 

Wright S. The Factors of the Albino Series in Guinea Pigs and their Effects on Black and Yellow Pigmentation. Genetics 1925;10:223. More about the C series of genes. Sepia cannot be graded in agouti animals. Sepia tones darken with age.

Iljin NA. Ruby Eye in Animals and Its Heredity. Trans Lab Exper Biol, Zoo Park, Moscow 1926;1:1. Inaccessible paper cited by Wright in Burdette, 1963. Described a P series allele Pr which resulted in lighter eye color but no change in coat color.

Wright S. The Effects in Combination of the Major Color Factors in the Guinea Pig. Genetics 1927;12:530. First full description of Fader.

Wright S. The Physiology of the Gene. Physiological Reviews 1941;21:487. Quantitative determination of melanin in the various phenotypes.

For sale on Amazon October 2001:

Sewall Wright and Evolutionary Biology (Science and Its Conceptual Foundations) by William B. Provine (paperback 1989)
University of Chicago Press; ISBN: 0226684733

Anatomy of the Guinea Pig -- by Gale Cooper, Alan L. Schiller (Contributor); Hardcover Our Price: $73.50 

The Guinea Pig : Healing, Food, and Ritual in the Andes
by Edmundo Morales
List Price: $19.95
 (August 1995) 
University of Arizona Press; ISBN: 0816515581

http://www.stat.wisc.edu/wright/wright/
Who was Sewall Wright? Web site

http://www.harvardsquarelibrary.org/unitarians/wright-sewall.html
another Sewall Wright Web site, with biography