Mouse coat color genetics: Agouti, albino and lethal yellow
Table of contents
Level: School to college · Start here: mouse coat color calculator
Mouse coat color genetics is one of the places where animal genetics began. Soon after Mendel’s work was rediscovered in 1900, the French biologist Lucien Cuénot used mice to show that Mendel’s laws apply to animals as well as plants. A century later, the same handful of coat genes still teach dominance, multiple alleles, lethal alleles, epistasis and natural selection, and mice remain one of the most widely used animals in genetics research.
This is CrossCalc’s mouse genetics section. If you’ve come from cat genetics, you’ll recognize several of the genes: cats and mice share the agouti, albino (TYR) and white-spotting (KIT) genes.
Pages in this section
Tool
- Mouse coat color calculator: choose genes for two mice and see the chance of each pup coat, with the lethal boxes crossed out.
Coats and crosses
- Lethal yellow mice: why two yellow mice give a 2:1 ratio, and how the puzzle was solved. High school to college.
- White mice: albino lab mice, the 9:3:4 epistasis ratio, and other kinds of white mice. School to high school.
Mice in research and evolution
- Beach mouse evolution: sand-colored coats, the Mc1r and Agouti genes, predator experiments and rock pocket mice. High school to college.
- Mouse methylation inheritance study: a 2026 study of chemical marks on DNA that didn’t follow Mendel’s laws. In the news; high school (advanced) to college.
What each gene teaches
| Gene | What you see | Genetics idea it teaches |
|---|---|---|
Agouti (Ay > A > a) | Yellow, agouti (wild-type) or solid | Multiple alleles; a lethal allele (Ay/Ay) and the 2:1 ratio |
Brown (Tyrp1, B > b) | Black vs brown | Simple dominance |
Albino (Tyr, C > c) | White with pink eyes | Recessive epistasis: c/c hides every other color gene (9:3:4) |
Dilute (Myo5a, D > d) | Paler coat | A recessive modifier of other colors |
Pink-eyed dilution (Oca2, P > p) | Pale coat, pink eyes | A recessive gene that also affects eye color; linked to albino on chromosome 7 |
Piebald (Ednrb, S > s) | White patches | Variable expression: the amount of white differs between mice with the same genotype |
Three quick examples
Two yellow mice. They give 2 yellow pups to every 1 black, not 3:1, because Ay/Ay embryos die before birth. (See why.)
Two black mice with an albino pup. Both parents carry c (C/c), and the pup is c/c. Each pup had a ¼ chance of being albino, the same 3:1 logic as a monohybrid cross.
An agouti mouse from two black parents? Not through the agouti gene. Black mice are a/a, so they can only pass on a. An agouti pup needs an A from a parent that has one.
Why mice, and what to watch for
Mice breed fast, litters are big, and inbred strains let researchers compare genetically identical animals. That’s why a few coat genes discovered in pet “fancy” mice became some of the best-understood genes in biology.
- The calculator model is simplified. Real mice have more alleles at most of these genes, and some genes are linked rather than inherited independently.
- Some coat genes affect more than color. Lethal yellow mice tend to become obese, and albino mice see less well than pigmented mice. CrossCalc describes these effects factually; it doesn’t give breeding or care advice.
Across species: mouse genes in cats, horses and people.
- Agouti (ASIP): lethal yellow mice, tabby versus solid cats, and bay versus black horses.
- TYR: albino mice, Siamese cats, and oculocutaneous albinism in people.
- MC1R: beach mice and rock pocket mice, red hair in people and chestnut horses.
- KIT: white-spotted mice, dominant white cats and white or patterned horses.
- Dilute: mouse dilute (Myo5a) and leaden (Mlph); dilute cats carry an MLPH change.
Related
- Cat genetics: the cat section, with many of the same genes
- Beyond Mendelian inheritance: lethal alleles, epistasis and more
- Dihybrid cross calculator: any two- or three-gene cross
- Genetics glossary: plain definitions of allele, locus, genotype and more
Sources
- Wolfe HG, Coleman DL. “Pigmentation.” In Biology of the Laboratory Mouse, Chapter 21. The Jackson Laboratory, via Mouse Genome Informatics. informatics.jax.org/greenbook
- Michaud EJ, et al. “A molecular model for the genetic and phenotypic characteristics of the mouse lethal yellow (Ay) mutation.” PNAS 91, 2562–2566 (1994). doi:10.1073/pnas.91.7.2562
- Castle WE, Little CC. “On a modified Mendelian ratio among yellow mice.” Science 32, 868–870 (1910). doi:10.1126/science.32.833.868
- Hoekstra HE, et al. “A single amino acid mutation contributes to adaptive beach mouse color pattern.” Science 313, 101–104 (2006). doi:10.1126/science.1126121