Bird Genetics Calculator

Genotype and phenotype: the two things people mix up

Phenotype is what you see: the color, the pattern, the eye color. Genotype is the pair of alleles the bird actually carries at a locus. Two birds can look identical and carry completely different genotypes.

That gap is the whole reason a genetics calculator exists. A normal green budgerigar and a normal green budgerigar split for blue are the same phenotype. Only their genotypes differ, and only their chicks reveal it.

Some mutations narrow the gap. In a canary, dominant white is expressed whenever the factor is present, so a plain-looking canary cannot be hiding it. Recessive traits do the opposite and hide easily for generations.

What "split" actually means

A split bird carries one copy of a recessive mutation and one wild-type copy at the same locus. It looks normal. It passes the mutant allele to roughly half its chicks, which is why splits quietly move a mutation through an aviary.

You cannot see a split. No photograph, feather sample or hands-on inspection reveals it. Split status is established in three ways only: parentage records that force the conclusion, a test pairing to a visual bird, or a validated DNA test where one exists for that specific mutation.

There is one clean exception, and it is the most useful fact in bird genetics. A hen cannot be split for a sex-linked trait. She carries a single Z chromosome, so she is either visual for that trait or genetically clear of it.

Sex-linked inheritance in birds

Birds do not use the mammalian XY system. Cocks are ZZ and hens are ZW. The Z chromosome carries genes; the W carries very few. Every sex-linked color mutation in these species sits on the Z.

The consequences are specific and testable:

• A cock needs two copies to be visual, and with one copy he is split and looks normal.
• A hen needs one copy to be visual, and she cannot carry a hidden copy.
• A hen passes her Z to her sons and her W to her daughters.
• Daughters therefore inherit a sex-linked trait from their father only.

This produces results that surprise breeders. Pair a visual sex-linked cock to a normal hen and every daughter is visual while every son is only split. Reverse the sexes and no chick is visual at all.

It also means confirmed sex is not optional. Without DNA sexing or another reliable method, a sex-linked calculation is arithmetic performed on a guess, which is why the calculator refuses to run one.

Autosomal recessive inheritance

An autosomal locus sits on a chromosome that both sexes carry in pairs. A bird needs two copies of the mutant allele to be visual, one copy makes it split, and cocks and hens have exactly the same chances.

The familiar figures follow from that. Split to split gives a one in four chance per chick of a visual bird, and two out of the three non-visual outcomes are splits. Visual to split gives one in two. Visual to visual gives every chick visual.

The trap is the middle result. Split to split leaves you with normal-looking chicks that are twice as likely to be split as clear, and nothing about them shows which is which.

Autosomal dominant and incomplete dominant inheritance

With a complete dominant such as budgerigar dominant gray or dominant pied, one factor is enough to show the trait, and single and double factor birds look alike. A visual bird of unknown factor is genuinely ambiguous, so the calculator reports both cases separately.

With an incomplete dominant, sometimes called co-dominant, the two are visually different. Budgerigar dark factor gives light, cobalt and mauve for zero, one and two factors. Spangle gives a normal, a single factor spangle and a very different double factor bird.

That difference matters practically. Incomplete dominance lets you read the genotype off the bird, which removes an entire layer of uncertainty from your planning.

Why probability is per chick, never per clutch

A 25 percent result does not mean one chick in four. It means each chick independently has a one in four chance, in the same way four coin tosses can land four heads.

In a clutch of four at 25 percent per chick, roughly 32 percent of clutches contain no visual chick at all, and a small share contain three or four. The average across many clutches is one. Any single clutch is a sample, not a distribution.

The optional clutch figure in the calculator exists to make this concrete. It shows a long-run average and the chance of at least one, and it deliberately never states what your next clutch will produce.

Why the same mutation name behaves differently across species

Mutation names travel between species faster than evidence does. A name describes an appearance. Inheritance is a property of a locus in one species, and it has to be established there by breeding records.

Three documented examples show why a universal predictor fails:

The lovebird case is the sharpest. Sex-linked ino and NSL ino produce birds that only a trained eye separates, yet one is inherited from the father's Z chromosome and the other needs two autosomal copies. Guess wrong and every prediction inverts.

Limitations you should assume are in force

• One locus at a time. Combination varieties such as pineapple, albino cockatiel, lacewing or creamino are two or more loci and are returned as not modeled.
• Independent loci. The tool does not model linkage or crossover between sex-linked genes sitting on the same Z chromosome.
• No modifiers. Expression of pied, pearl, spangle and similar traits varies with modifier genes that no simple model captures.
• No fertility or survival modeling. Probabilities describe chicks that hatch, not hatch rates, embryonic loss or chick survival.
• Phenotype error is your risk. A lightly marked pied, a molted-out pearl cock or a misidentified pallid feeds a wrong answer into a correct model.
• Species-limited. Conure modeling covers green-cheeked conures only. Other conure species are excluded because their mutation inheritance is not documented well enough.
• Living science. Where inheritance is disputed, such as rosy-faced orange face and gray factor, or the double factor dominant white canary, the trait is excluded or flagged rather than scored quietly.

Breeder records that make the numbers mean something

The calculator is only as good as what you feed it, and the input it most often lacks is a reliable genotype. Records fix that, and nothing else does.

Unexpected chicks are the most valuable entries you will ever make. A visual chick from two apparently normal parents tells you more about your stock than a season of expected results.

Welfare and ethical breeding

Color is a poor reason to make a pairing on its own. Health, temperament, parenting ability and genetic diversity all rank above appearance, and a probability table has nothing to say about any of them.

Three concrete cautions come from the evidence base behind this page:

• Recessive white canaries carry a defect in carotenoid uptake and their vitamin A supply has been studied specifically in the veterinary literature. Discuss diet with an avian veterinarian before breeding them.
• Canary practice pairs crested birds to plain-headed birds only. The comparable crest trait in domestic chicken links homozygosity to skull malformation, and the calculator refuses to score crested to crested.
• Lutino cockatiels commonly show a bald patch behind the crest. Select parents with good feather cover there rather than breeding the fault forward.

Chasing rare recessives concentrates relatedness quickly, because the shortest route to a visual bird usually runs through close relatives. Track inbreeding, bring in unrelated birds, and stop a line that produces repeated defects.

Plan the outcome, not just the pairing. Know where every chick will go, including the normal-looking ones that make up most of a clutch and are the hardest to place.

When to consult an avian veterinarian or a genetics specialist

Contact an avian veterinarian when a pairing produces repeated infertility, dead-in-shell chicks, or chicks with physical abnormalities; when a hen shows signs of egg binding or reproductive disease; or before breeding any bird with a known metabolic or nutritional condition.

Get species-specific veterinary input before breeding a mutation with a documented health association, and before making major diet changes for a breeding pair. General bird care advice does not substitute for it.

Contact a breed society or an avian genetics specialist when results repeatedly contradict the model, when you are trying to identify which of two similar mutations you hold, or when you may have found something new. Trial pairings recorded properly are how mutation inheritance gets established.

Methodology

Each species and trait pair is assigned one documented inheritance mode: sex-linked recessive, autosomal recessive, autosomal dominant, or autosomal incomplete dominant. No mode is carried across species by analogy, and no trait is included without a source.

Autosomal outcomes use a standard two-allele gamete calculation. A parent with zero, one or two mutant copies contributes the mutant allele with probability 0, 0.5 or 1, and the two gametes combine independently.

Sex-linked outcomes model the ZW system directly. The father's Z allele is drawn from his two copies, sons receive one Z from each parent, daughters receive their single Z from the father, and chick sex is taken as an even split.

Unknown genotypes are never averaged. Where a parent's status is ambiguous, every consistent genotype is enumerated and reported as a separate scenario, so the honest answer stays visible as a set of conditional results.

Traits are excluded where evidence is contested, where the variety is a combination of loci, or where only a trade name exists. Excluded cases return "not modeled" with the reason, rather than a number.

Frequently asked questions

Sources

• Cooke TF et al. Genetic mapping and biochemical basis of yellow feather pigmentation in budgerigars. Cell, 2017. View
• Mundy NI. Coloration genetics: pretty polymorphic parrots. Current Biology, 2018, confirming budgerigar blue as an autosomal recessive allele. View
• Online Mendelian Inheritance in Animals, OMIA 001701-13146, feather color blue in Melopsittacus undulatus. View
• Toomey MB et al. High-density lipoprotein receptor SCARB1 is required for carotenoid coloration in birds. PNAS, 2017, identifying the recessive white canary mutation. View
• Online Mendelian Inheritance in Animals, OMIA 001252-9135, recessive white in Serinus canaria. View
• Gazda MA et al. A genetic mechanism for sexual dichromatism in birds. Science, 2020, on the canary mosaic trait. View
• Gazda MA et al. Genetic basis of de novo appearance of carotenoid ornamentation in bare parts of canaries. Molecular Biology and Evolution, 2020, on urucum. View
• Preuss SE et al. Vitamin A requirements of alipochromatic recessive-white and colored canaries during the breeding season. Veterinary Record, 2007. View
• Wolf P et al. Vitamin A metabolism in recessive white canaries. Animal Welfare, 2000. View
• Sato K et al. Multiple mutations in polyketide synthase disrupting psittacofulvin production across parrot species. Communications Biology, 2025, covering lovebirds as well as budgerigars. View
• Van den Abeele D, Ornitho-Genetics VZW and MUTAVI. Agapornis roseicollis: dilute versus pallid, establishing pallid as sex-linked recessive and allelic with sex-linked ino. View
• Van den Abeele D, Ornitho-Genetics VZW. Pallid in Agapornis fischeri. View
• Van den Abeele D, Ornitho-Genetics VZW. Fallow mysteries, on autosomal recessive fallow inheritance and non-allelic fallow types. View
• Van den Abeele D, Ornitho-Genetics VZW. Update on gray in Agapornis roseicollis, the basis for excluding gray factor and orange face from this tool. View
• American Federation of Aviculture, Watchbird. Green-cheeked conures, establishing cinnamon and opaline as sex-linked. View
• Pyrrhuras.net. Breeding record of the first lutino Pyrrhura molinae, establishing autosomal recessive inheritance. View
• American Federation of Aviculture, Watchbird. Cockatiel genetics. View
• American Federation of Aviculture, Watchbird. Recent mutations in cockatiels, on dominant silver. View
• American Federation of Aviculture, Watchbird. Dominant white canary, reviewing and disputing the double factor lethal theory. View
• Wragg D et al. The crest phenotype in chicken is associated with ectopic expression of HOXC8, and homozygosity with cerebral hernia. View
• Association of Avian Veterinarians, bird owner resources and vet directory. View
• Martin T. A Guide to Color Mutations and Genetics in Parrots. ABK Publications, 2002. Print reference for budgerigar and parrot mutation modes.
• Perez-Beato O. Fundamentals of Color Genetics in Canaries. RoseDog Books, 2008. Print reference for canary mutation modes.