Db), Melanotic (Ml) and Pattern (Pg) sit close together on the same chromosome, so they are usually inherited as a set. That linkage is a big part of why a pattern like mille fleur holds together, and it is built into how the Breeding Outcomes tool calculates a cross. For the wider system, see the Genetics Guide.
The three genes
Each of the three does a different job in building a pattern — for what they do, see the pattern genes page. This page is about how they inherit.
| Gene | What it contributes |
|---|---|
Dark Brown (Db) | Deepens and shifts the gold/red ground colour. |
Melanotic (Ml) | Adds and extends black through the plumage. |
Pattern (Pg) | Organises the black into structured markings — lacing, spangling and the like. |
Why linkage matters
Genes that sit close together on a chromosome do not assort independently — they travel together far more often than chance would allow. Db maps to the SOX10 region and Ml to the GJA5 region of chromosome 1, with Pg showing strong empirical linkage to both.1 Only an occasional crossover during meiosis reshuffles them:
| Pair | Estimated recombination |
|---|---|
Db ↔ Ml | ~12% |
Ml ↔ Pg | ~10% |
Db ↔ Pg | ~22% |
In practice that means roughly 85% of a bird's gametes carry the parental combination of these three intact, where three unlinked genes would keep the same combination only about a quarter of the time.2 The trio behaves almost like a single unit.
In mille fleur
Mille fleur's genotype is eb/eb · Db/Db · Pg/Pg · Ml/Ml · mo/mo — and three of those five defining genes are exactly this linked group. Because Db, Pg and Ml ride together on chromosome 1, a mille fleur bird usually passes them on as a package rather than as three independent throws. That is a large part of why the pattern travels reliably through a line once it is fixed, and why related varieties — Tollbunt, porcelain — are built by swapping or adding a single gene around that same stable core.
How the Breeding tool handles it
The Breeding Outcomes tool marks Db, Ml and Pg with a small † and, when a cross involves more than one of them, shows a linked-gene note. The individual Db/Ml/Pg Punnett squares each show their own locus at the standard Mendelian ratios — but the combined F1 Genotype Frequencies table further down applies the actual linked recombination ratios by default.2 So the frequencies you read off already account for the linkage, instead of pretending the three genes assort freely.
Db/db+ · Pg/pg+ · Ml/ml+) comes out around 8% under real linkage versus about 3% if the three genes assorted independently, and the fully-homozygous-mutant class (Db/Db · Pg/Pg · Ml/Ml) — which looks like it should be a rare double recombinant — is actually about 4% under linkage versus well under 1% independent, because that combination is the intact, non-recombined haplotype inherited whole from the Porcelain parent.
- Molecular mapping of the linked
Db/Mlpattern loci on chromosome 1 (SOX10 / GJA5 regions): Schwochow, D., et al. (2021) Pigment Cell & Melanoma Research; Sandve, S. R., et al. (2021) PNAS. See the pattern genes references. - The recombination-frequency estimates and the linked-ratio calculation are those used by the Breeding Outcomes tool, consistent with the chicken genetic map: International Chicken Genome Sequencing Consortium (2004) Nature 432:695–716.