Pattern Genes: Lacing, Pencilling & Spangling

Lacing, pencilling, spangling, barring — the crisp markings that define so many varieties — are not each a separate "pattern gene". They mostly come from one gene, the Pattern gene, whose result depends entirely on the base it is working on and the company it keeps. That dependence is the clearest everyday example of epistasis, and understanding it explains a lot of varieties at once. For the wider system, see the Genetics Guide.

Close-up of gold-and-black double-pencilled Brahma feathers, each showing concentric dark bands that follow the feather's outline. — Double pencilling: dark bands repeat as concentric outlines within each feather. Partridge Brahma hen.

Close-up of red-gold Brahma feathers, each edged with a solid black border. — Lacing: a single crisp dark border rims each feather. Black-laced-red Brahma.

Buff hen with pale lace edging scalloped around each feather over the back and wings. — Lacing reads light-on-dark here instead: a pale, near-white edge around a buff ground.

Close-up of buff wing feathers, roughly half buff and half white, edged with a pale lace border. — Same organising pattern, a different ground and edge colour — lacing is the arrangement, not one fixed palette.

Pattern genes organise black — they don't create it

The pigment is already there: the Extension base sets how much eumelanin (black) a bird has and where it starts. Pattern genes then arrange that black into shapes. The three that do most of the work are:

Pattern gene (Pg) — the organiser; on its own it breaks black into barring or pencilling, and in combination it produces lacing and spangling.
Columbian (Co) — clears black off the body and confines it, which turns diffuse black into a defined edge.
Melanotic (Ml) — adds black, which is what turns single lacing into double.

None of these means anything fixed on its own. The same Pg gives a completely different bird depending on which base and partners it has — so you cannot read it in isolation.

The same gene, four patterns

Here is the dependence laid out. Read it as "this combination → this pattern":

Pattern	Combination	Look
Pencilling / barring	`Pg/Pg` on a partridge base, on its own	Fine concentric lines or bars across each feather.
Single lacing	`e^b` + `Pg/Pg` + `Ml/Ml` + `Co/Co`	A clean dark border around a feather of ground colour.
Double lacing	`e^b` + `Pg/Pg` + `Ml/Ml` (no Columbian)	Two concentric borders — the extra black from Melanotic.
Spangling	`e^R` (birchen) + `Pg/Pg`	A dark spot or crescent at each feather tip.

Swap the base under a fixed Pg and the pattern changes; add or remove Co or Ml and it changes again. Lacing is really "Pattern gene, restricted to the edge by Columbian, on a brown base" — spell out the parts and the finished bird stops being mysterious. (Note that the autosomal barring the Pattern gene can produce is a separate thing from the sex-linked Barring gene, B, which lays the crisp cuckoo bars and is inherited on the Z chromosome.)

One copy vs two copies. The /Pg or /Ml shorthand above always means two copies (homozygous) — that's what a clean, complete pattern needs. One copy of Pg alone tends to give incomplete, patchy marking rather than full rings or bars; one copy of Ml on an otherwise-lacing base tends to leave the lacing incomplete too, often only at the feather tip. Columbian behaves a little differently: one copy clears black more strongly in roosters than in hens, and two copies are normally needed for an even pattern in both sexes. The Breeding Outcomes tool spells out which of these apply to a specific cross.

Why this is epistasis. Epistasis is when one gene's visible effect depends on the alleles at another gene. Pattern genes are the textbook case: Pg has no single "look" of its own — its result is decided by the Extension base and by Co/Ml alongside it. This is why two birds can both "carry the pattern gene" and look nothing alike, and why building a laced variety means assembling several genes in the right combination, not flipping one switch.

Building a patterned variety

Because a pattern is a combination, creating or fixing one is a multi-locus project: you need the right base and the right pattern partners, several of them homozygous at once. A single cross rarely lands the whole combination; the pattern usually assembles over generations as the pieces come together. Laying out which loci differ between your birds — and what a cross will actually combine — is exactly what the tools are for: Compare Standards shows which loci separate two varieties, and Breeding Outcomes works out what a mating combines, including the linked Db–Ml–Pg group.

Individual pattern terms — lacing, pencilling, spangling, barring, and the genes behind them — are defined in the glossary.

References & notes

Pattern-gene combinations and the Extension base framework: Smyth JR Jr (1990) Genetics of plumage, skin and eye pigmentation in chickens, in Crawford RD (ed.) Poultry Breeding and Genetics, Elsevier.
Molecular mapping of the linked Db/Ml pattern loci on chromosome 1: Schwochow D et al. (2021) Pigment Cell & Melanoma Research; Sandve SR et al. (2021) PNAS. Full list in the Genetics Guide references.

Try it: plan a patterned cross · read the Genetics Guide · browse the glossary