Grey Factor Budgerigar Mutation, Complete Genetics Guide

One of the most popular budgerigar exhibition mutations worldwide. Autosomal incompletely dominant, Grey factor adds a grey wash that combines additively with both blue-series and green-series base colors. Sky Blue + Grey produces the standard Grey. Cobalt + Grey produces Dark Grey. Light Green + Grey produces Grey Green. Single Factor and Double Factor expressions differ subtly in saturation.

Written by Ayaan Shohan

Founder, KinBird Aviary · Bangladesh

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What Grey factor looks like on a real bird

A Grey factor budgerigar has a grey wash overlaid on its base colour. The wash is most visible on the body feathers and the cheek patches.

On Sky Blue base, Grey factor produces a bird called simply Grey — uniform grey body with grey cheek patches (rather than the violet cheek patches of Normal Sky Blue). On Cobalt base, Grey factor produces Dark Grey. On Mauve base, Grey factor produces Mauve Grey.

On green-series birds Grey factor produces Grey Green colouration. Light Green + Grey = Grey Green. Dark Green + Grey = Dark Grey Green. Olive Green + Grey = Olive Grey Green.

The tail feathers in Grey factor birds are black with grey margins. The wing markings, throat spots, and other melanin features are unaffected.

How Grey factor inheritance works

Grey factor is autosomal incompletely dominant. The gene sits on an autosome and inherits identically in cocks and hens. A bird can be Normal (no Grey allele), Single Factor or SF (one copy), or Double Factor or DF (two copies).

SF Grey × SF Grey produces the textbook 1:2:1 Mendelian ratio: 25% Normal, 50% SF Grey, 25% DF Grey offspring.

DF Grey × Normal produces 100% SF Grey offspring.

DF Grey × DF Grey produces 100% DF Grey offspring.

The SF vs DF distinction is subtler than for some other incompletely dominant mutations. Most exhibition standards classify SF and DF Grey together as Grey for judging.

Grey factor combined with dark factor

Grey factor stacks predictably with dark factor for the standard naming convention.

Sky Blue + Grey = Grey (exhibition convention drops Sky Blue from the name).

Cobalt + Grey = Dark Grey.

Mauve + Grey = Mauve Grey.

Light Green + Grey = Grey Green.

Dark Green + Grey = Dark Grey Green.

Olive Green + Grey = Olive Grey Green.

The Budgerigar Genetics Calculator follows the exhibition naming convention, outputting these combined names rather than the longer parenthetical forms.

Grey combinations with other mutations

Grey factor combines productively with nearly every other budgerigar mutation.

Grey Opaline is one of the most popular exhibition pairings worldwide.

Grey Cinnamon produces grey body with brown wing markings — a chalky, soft-toned exhibition phenotype.

Grey Spangle combines reverse wing markings with grey body. SF Spangle SF Grey is a popular show combination.

Grey Violet on Cobalt produces a violet-tinged dark grey body.

Grey Yellow Face on blue series adds yellow face to a grey body.

Grey Black Face combines the grey body with the heavy black face mask of Black Face — extremely rare.

Grey × Grey, the 1:2:1 demonstration

Two SF Grey birds paired together produce the textbook autosomal incompletely dominant 1:2:1 ratio: 25% Normal offspring, 50% SF Grey offspring, and 25% DF Grey offspring.

This is one of the cleanest exhibition demonstrations available because Grey factor's visible expression is well-understood and the percentages match observation directly.

For breeders wanting to fix Grey factor into a line at DF level, pair DF Grey × DF Grey to produce 100% DF Grey offspring. For breeders wanting maximum SF Grey output, pair DF Grey × Normal to produce 100% SF Grey offspring.

History and origin

Grey factor budgerigars have been documented since the late 1930s, with stable Grey lines appearing in both Australia and the UK in close succession. The mutation entered exhibition lines during the 1940s as breeders recognized that Grey was distinct from the existing Slate sex-linked mutation.

By the 1950s Grey was an established WBO exhibition class. The mutation is now present in every serious exhibition aviary worldwide, often combined with other mutations like Opaline or Cinnamon to produce show-line pairings.

Grey vs Slate, the two grey-producing mutations

Grey factor (autosomal incompletely dominant) is sometimes confused with Slate (sex-linked recessive), as both produce grey appearance.

Grey factor is autosomal, expressed identically in cocks and hens, with clear SF vs DF distinction. Grey factor produces a uniform medium grey across the body and grey cheek patches.

Slate is sex-linked recessive (Z chromosome). Cocks can be split for Slate; hens cannot. Slate produces a slightly different grey tone, often with a slate-blue tint visible on close inspection.

Grey factor is far more common in exhibition lines. Slate remains rare. The Budgerigar Genetics Calculator handles both mutations independently.

Grey factor pairing predictions in the calculator

The Budgerigar Genetics Calculator handles all Grey factor pairings including the SF vs DF Mendelian ratios, combinations with dark factor for proper base color naming, and combinations with all other mutations.

Try SF Grey × SF Grey for the textbook 1:2:1 ratio. Try DF Grey Green × Light Green to see the green-series combination. Test any pairing instantly at budgerigargenetics.com.

Frequently asked questions about grey factor

What is the Grey factor in budgerigars?

Grey factor is an autosomal incompletely dominant budgerigar modifier. It adds a grey wash to the body and changes the cheek patches from violet to grey. The tail feathers darken from black to black with grey margins. Grey factor combines additively with both blue-series and green-series base colors.

How does Grey factor combine with base colors?

Sky Blue + Grey = Grey. Cobalt + Grey = Dark Grey. Mauve + Grey = Mauve Grey. Light Green + Grey = Grey Green. Dark Green + Grey = Dark Grey Green. Olive Green + Grey = Olive Grey Green. The Budgerigar Genetics Calculator follows the exhibition naming convention.

What is the difference between SF Grey and DF Grey?

SF Grey is a clean medium grey; DF Grey is a slightly more saturated grey. The visual difference is subtler than for some other incompletely dominant mutations. Most exhibition standards classify SF and DF Grey together for judging.

What does SF Grey × SF Grey produce?

The textbook 1:2:1 Mendelian ratio: 25% Normal offspring, 50% SF Grey offspring, and 25% DF Grey offspring. This is one of the cleanest demonstrations of autosomal incompletely dominant inheritance available.

What is the difference between Grey factor and Slate?

Grey factor is autosomal incompletely dominant — expressed identically in cocks and hens. Slate is sex-linked recessive — cocks can be split, hens cannot. Grey factor is far more common in exhibition lines. Slate remains rare. The Budgerigar Genetics Calculator handles both mutations independently.

Can Grey combine with Opaline, Cinnamon, or Spangle?

Yes. Grey Opaline is one of the most popular exhibition combinations worldwide. Grey Cinnamon produces a chalky grey body with brown wing markings. Grey Spangle combines reverse wing markings with grey body. Grey Violet, Grey Yellow Face, Grey Black Face, and many other combinations all work.

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