crosscalc

Dilute cat genetics: Why blue, lilac and cream cats look pale

Published

Table of contents
  1. What the dilute gene does
  2. Why two black cats can have a blue kitten
  3. More worked crosses
  4. Blue × black carrier: d/d × D/d
  5. Chocolate carriers: b/b D/d × b/b D/d
  6. Dilute with the X-linked orange gene
  7. Blue cat breeds
  8. Common questions
  9. Is blue a separate color gene?
  10. Does dilute affect orange cats too?
  11. Is a gray tabby a dilute cat?
  12. Can a D/D parent have blue kittens?
  13. Practice
  14. Where the model stops
  15. Related
  16. Sources

Level: School to high school · You’ll need: dominant and recessive alleles and a monohybrid cross · Part of cat genetics

Dilute cat genetics is a single recessive allele. A cat with two copies of the dilute allele d (genotype d/d) has its color softened: black becomes blue (gray), chocolate becomes lilac, cinnamon becomes fawn, and orange becomes cream. A cat with at least one D shows full-strength (“dense”) color.

Assumptions for the crosses on this page: one dilute gene with two alleles (D dominant, d recessive), other genes held the same, and enough kittens for the ratios to show.

What the dilute gene does

The gene is MLPH (melanophilin). Its protein helps move pigment packets (melanosomes) from pigment cells into the growing hair. In a d/d cat the protein doesn’t work, so the pigment ends up in uneven clumps inside each hair instead of spread evenly. The hair holds the same kind of pigment, but it absorbs less light and looks paler.

That’s why dilution changes every color in a matching way:

Dense color (D/D or D/d)Dilute color (d/d)
BlackBlue (gray)
ChocolateLilac (pale pinkish gray)
CinnamonFawn
Red (orange)Cream
TortoiseshellBlue-cream (dilute tortoiseshell)
CalicoDilute calico

Dilute is a modifier: it doesn’t make a color of its own; it changes the color other genes produce. That makes it a good first example of genes working together.

Why two black cats can have a blue kitten

Because d is recessive, a black cat can carry it hidden (D/d). Two carriers give the familiar 3:1 ratio:

Dd
DD/D blackD/d black (carrier)
dD/d black (carrier)d/d blue

¾ black, ¼ blue. Check it in the calculator.

Seeing a blue kitten tells you something useful: both parents carry d, even if they’re both black.

More worked crosses

Blue × black carrier: d/d × D/d

Half the kittens get d from the black parent: ½ black, ½ blue. This is a test cross pattern: crossing with the recessive type reveals whether the other parent carries d. Check it.

Chocolate carriers: b/b D/d × b/b D/d

Same 3:1, different colors: ¾ chocolate, ¼ lilac. The dilute gene treats chocolate exactly the way it treats black.

Dilute with the X-linked orange gene

A blue-cream female (XᴼXᵒ d/d) and a blue male (XᵒY d/d) are both d/d, so every kitten is dilute. The Orange gene then splits by sex, as on the calico page:

  • Daughters: ½ blue-cream, ½ blue
  • Sons: ½ cream, ½ blue

Check it. Cream sons show faint tabby markings even without the agouti allele, like all orange-based fur.

Blue cat breeds

Some breeds are recognized only in blue by most registries, which means every cat in the breed is d/d and black-based: the Russian Blue, Chartreux and Korat. The British Shorthair is best known in blue but comes in many colors. In these breeds, two blue parents can only have blue kittens through this gene.

Common questions

Is blue a separate color gene?

No. Blue is black plus d/d. There’s no “blue allele” at the color gene.

Does dilute affect orange cats too?

Yes. Cream is diluted red; blue-cream is a diluted tortoiseshell.

Is a gray tabby a dilute cat?

Usually not. Many gray-looking tabbies are black (brown) tabbies, whose banded hairs look gray from a distance. Silver tabbies look gray too but aren’t dilute either. True dilute tabbies are blue tabbies, with soft blue-gray stripes on a pale ivory background with fawn tones.

Can a D/D parent have blue kittens?

No. Every kitten gets a D from that parent, so none can be d/d.

Practice

  1. Two blue cats have kittens. What fraction will be blue?
  2. A black female has a blue kitten with a black male. What are both parents’ genotypes at the dilute gene?
  3. A cream male (XᴼY d/d) is crossed with a black female (XᵒXᵒ D/d). What colors are expected among the sons?
Answers
  1. All of them. Both parents are d/d, so every kitten is d/d.
  2. Both are D/d. The blue kitten (d/d) received a d from each parent.
  3. Sons get their X from their mother, so none are orange-based. Half get d from the mother and d from the father: ½ black, ½ blue.

Where the model stops

  • Other pale shades exist. Breeders also describe a “dilute modifier” said to turn blue, lilac and cream into caramel and apricot shades. Its genetics haven’t been confirmed by DNA studies.
  • Shade varies. Two blue cats can differ in tone because of other genes and coat texture.

Sources

Try it: work out any cross with the cat coat color calculator, or a general one with the Punnett square calculator.