Chicken Genetics

The sex-linked barring gene creates a pattern of white bars across each feather of the bird. Chicks will be mostly dark grey, with a small white patch on the back of the head. It is most commonly seen in barred, crele, and cuckoo varieties in numerous breeds.

It is both sexlinked and autosexing, meaning that it can be crossed with other varieties in a specific way to create sexable-at-hatch chicks, and that barred chicks can be sexed at hatch as well. Males will tend to have a bigger white spot on the back of their head than females.

The APA recognizes the following breeds with the barring gene: Cochin, Holland, Japanese, Plymouth Rock, d'Anver, Old English Game, Dominique.

Birchen is a popular base pattern on the E locus in chickens. It causes the bird to have a black body with gold edging through the head and hackles, with males having more red through the cape and saddle as well. Both sexes will have some lacing going down into the breast. Birchen itself often has other genes added on to create an all-black bird, or covered up with other genes to create spangling, lacing, barring, and more patterns.

In order of dominance, it is less dominant than Extended Black, but more dominant than any other mutation on the E locus, including the natural duckwing/wildtype.

Birchen by itself is recognized in American Game, bantam Cochins, Modern Game, and bantam Old English Game. It can be used to create many other accepted varieties as well.

Blue is most commonly known for the "blue, black, splash" genetics, as it presents two distinct forms. It is the most common and often only way to achieve the blue or splash variety in any breed.

In heterozygous form (one copy of blue), the bird will appear a slatey-blue color. It is most often seen with a slight lacing of darker blue or black (found with the lacing gene). In homozygous form (two copies of blue), the variety is called splash and will be a light grey or white undercolor, with spots of black or blue feathers across the body. The absence of either form of blue is usually black.

The APA recognizes the blue variety (heterozygous form) in Ameraucana, Andalusian, Cochin, Jersey Giant, Langshan, Orpington, Plymouth Rock, Sumatra, and Wyandotte.
However, it only recognizes splash (homozygous form) in Ameraucana, Cochin, and Modern Game.

The blue egg gene is an incomplete dominant gene in chickens that causes the bird to lay a beautiful blue colored egg. This is caused from an increase of Biliverdin deposited onto the egg in the shell gland.

With one copy of the gene, the egg with be a paler blue then the brilliant robin's egg color often seen with homozygous (two copies) of the gene. Blue egg can also be mixed with the brown egg gene to create green eggs in various shades. Birds will typically lay the most vibrant egg colors at the beginning of each reproductive cycle and lighten up as the season goes on.

Blue and green eggs in any shade do not have any impact on the overall nutritional value, egg size, egg shape, bird health, or general plumage traits, however the blue egg gene can cause the bird to lay less eggs overall.

The trait is most often seen in Ameraucanas and Araucanas, the only two recognized APA breeds to lay blue eggs, but can be bred into any breed. It is also a trait bred for in hatchery Americanas (Ameraucana crossbreds), Easter Eggers, Olive Eggers, Crested Cream Legbars, and Isrudds.

The buttercup gene is the gene behind the buttercup comb. It looks like two single combs that form a general cup or crown shape instead of the typical single comb.

The gene is linked to the general duplex comb locus, making it similar to the V-comb and other comb types where the typical single comb is split in two. A bird cannot have two copies of both the v-comb gene and the buttercup gene at the same time.

It is found on the Buttercup and Caumont breeds, though only the Sicilian Buttercup is recognized by the APA.

Chocolate is a sex-linked gene in chickens and ducks that causes the bird to be a deep, chocolate brown color. It is thought to be a similar mutation, though different inheritance, to the dark brown color seen in mice, cattle, sheep, pigs, cats, rabbits, and sheep, and the light color seen in quail and human hair.

Chocolate is sexlinked, meaning that it can be used to create a one-off batch where the chicks/ducklings can be sexed immediately at hatch. This is useful in hard-to-sex breeds like silkies.

Chocolate is not currently recognized by the APA in any chicken breeds, though it is recognized in Call, Muscovy, and Runner ducks.

The Columbian gene in chickens restricts the black pigment to the extremes of the bird - typically the wing tips, ends of the hackle feathers, and the ends of the tail will be black. It is an autosomal dominant gene, though some leakage may happen in the females with only one copy of the gene.

It is also used in combination with several other genes to create buff, laced, light, and other varieties.

The combless gene in chickens causes the bird to have a completely absent comb in the hens and very minimal comb in the males (usually just two small stubs across the top of the beak. It is completely recessive, and works only in combination with the duplex comb gene and likely the rose comb gene.

It is overall understudied due to the rareness of any combless chickens. The only breed known without a comb is the Breda fowl, which have been taken off the APA SOP due to inactivity, though there are currently a few breeders with the gene in the United States.

The crested gene creates a "poof" of feathers from the top of the skull in chickens. It is most commonly seen in Sultans, Polish, Houdans, and Silkies, though the shape of the crests vary wildly from breed to breed. This is due to the feather length, width, and shape that changes by breed.

Generally, the heterozygous forms of crested have smaller shaped crests, while the homozygous form has larger and more developed crests. Males will often have more prominent crest shapes than females in both forms.

The homozygous form of crest has also been linked to malformed skulls and head-shapes, though it is uncertain whether a second, linked gene is responsible for this or if it is due to the crested gene itself.

The APA recognizes Silkies, Sultans, Polish, Houdans, and Crevecoeur chickens to have crests.

Dilute is one of the lesser-studied genes in chickens. It causes the overall red coloration from gold or mahogany to be a lighter shade of orange. It is one of the genes used to make the Buff variety. More research needs to be done overall on the buff variety and dilute genes. It is likely incomplete dominant, though this hasn't been confirmed in any studies.

The APA recognizes Buff as a variety in the following breeds:
Ameraucana, Brahma, Catalana, Cochin, Cornish, Naked Neck, Orpington, Wyandotte, and Plymouth Rock, though Plymouth Rocks for sure do not utilize the dilute gene to create buff.

The rumpless gene causes the chicken to have no tail feathers. It removes the oil gland on the tail, all of the tail feathers, and either one or two of the last spinal vertebrae on the bird. It can also cause a fusing of some of the lower spinal column in some cases too. Breeds with natural rumplessness include the Araucana, Piao, Kaulhuhn, and d'Everberg chickens. All of these breeds often have decreased fertility and hatch rates, likely due to skeletal reproductive issues.

The mutation appears close to the same in both homozygous and heterozygous form, though most birds when tested are heterozygous, making many researchers believe that the homozygous form of the gene also causes lower hatch rates.

The APA recognizes only one rumpless breed: the Araucana.

Dominant white is a gene that restricts the black pigment in chickens. It causes the bird to keep all of the red tones, but none of the black.

The APA recognizes white in either dominant or recessive form in the following breeds: Ameraucana, American Game, Araucana, Aseel, d'Anver, d'Uccle, Booted Bantam, Chantecler, Cochin, Cubalaya, Dorking, Cornish, Favorelles, Hamburg, Holland, Houdan, Japanese, Jersey Giant, Lamona, Langshan, Leghorn (typically dominant white), Malay, Marans, Minorca, Modern Game, Naked Neck, Old English, Orpington, Plymouth Rock, Polish, Rhode Island White, Rosecomb, Serama, Silkie, Spanish, Sultan, Wyandotte and Yokohama.

Ermine and paint are unrecognized by the APA, though Ameraucana breeders are working to accept Ermine Ameraucana.

The Duplex Comb gene causes the chicken's comb to branch off into two separate combs towards the back of the skull. It interacts with the single comb, pea comb, and rose comb, but is on the same locus as the buttercup comb. This is the main gene that creates the "v-comb" seen in several breeds.

The APA recognizes the Crevecoeur, La Fleche, Houdan, Polish, and Sultan to have the duplex comb gene. Other breeds that naturally have the gene include the Appenzeller Spitzhauben and the Dutch Owlbeard.

Extended black is a base plumage in chickens. It is found on the E locus, and is the most dominant of all the bases. It causes an increased amount of eumelanin, or black pigment, in chickens, and is similar to the EB gene in coturnix quail and several mammals.

Chicks on with extended black bases typically are a dark grey to black color, with white patches through the front and breast. Chickens will often grow out with darker feathers, and black skin through the feet and beak of the bird if there aren't additional dilutions on top.

The APA currently recognizes black in the following breeds: Ameraucana, American Game, Australorp, d'Anver, Booted, Cochin, Cornish, Crevecoeur, Cubalaya, Dutch, Hamburg, Japanese, Java, Jersey Giant, LaFleche, Langshan, Malay, Modern Game, Old English Game, Orpington, Plymouth Rock, Rosecomb, Shamo, Sumatra, and Wyandotte (typically Partridge based). It is worth noting that is it possible to get black in these breeds without using the E base.

This gene causes black skin, eyes, organs, and some plumage colors in chickens. Contrary to some media, the fibro gene in chickens does not cause the chicken to also lay black eggs. It is most commonly seen in the Ayam Cemani and Silkie breeds, though it can be introduced into other crosses and has been recently seen in the Zombie Cross (Leghorn x Cemani).

It is considered an almost completely dominant gene, meaning that it is very hard to tell if a bird has only one copy or two copies of the gene, and all crosses will share similar characteristics (black skin, organs, eyes, etc.) It is not uncommon to see white toenails, lighter grey tongues, or other slight color leakage in homozygous or heterozygous form.

The APA only recognizes Silkies with black skin, though the Ayam Cemani Breeders Association is working to get APA recognition as well.

Frizzle is a feather modifier gene. In heterozygous form, it causes in the feathers to curl backwards across the body of the bird, with the tips of the feather pointing towards the head instead of lying flat. There are no health affects in the normal presentation of hetero. frizzle, aside from birds being more prone to the cold as they can't regulate their temperature as well.

In homozygous form, it presents as "frazzle", where the entire feather is so curled that the shaft becomes brittle. The feathers in a frazzle bird often cause pain to the bird as the feathers snap off frequently, and breeding for frazzle is considered inhumane.

It is recognized by the APA on any breed. It is most commonly found in bantam Cochins, Silkies, and Serama, though a few other breeds like d'Uccles and Favorelles have had frizzle introduced.

Henny feathering (often called hen feathering) is a mutation in chickens that causes the males to grow in female plumage. It is caused by an increased level of estrogen and decreased levels of testosterone in the feather and skin cells of the chickens, which prevents the long hackle and saddle feathers typically seen in males (called benny feathering).

It is an incomplete dominant trait. Male birds with only one copy of the gene will show higher levels of testerone in the skin, but still look almost completely henny feathered. Females with either form of the gene do not have any noticable differences.

The APA recognizes Sebrights and Campines, both breeds that require hen feathering in the males. Henny feathering has also been noted in Leghorns, and could be bred into any breed.

Lavender is a recessive mutation in chickens that causes the bird to become a washed out, light grey color. It is often called "self-blue", a term more generally used in exhibition poultry. Similar mutations (though different genes) are also seen in mice, humans, and quail. Lavender birds often have a slightly ragged look to their feathers, though it is unknown if this is caused by the gene itself or by the line of birds.

Lavender is not currently recognized by the APA in any breed, though "self-blue" is recognized in Ameraucana, d'Anvers, Booted, Old English Game, and Silkies.

Melanotic is a simple mutation in chickens that extended the overall black plumage color in chickens. Some patterning often comes through with melanotic alone, though it depends on the underlying base. The gene does not extend the black pigment to the skin, beak, or shanks, which will often stay the typical white color. It also doesn't change much of the overall chick down, so chicks with only Melanotic will typically stay a dark patterned color, and then feather out completely or nearly completely black.

The APA currently recognizes black in the following breeds: Ameraucana, American Game, Australorp, d'Anver, Booted, Cochin, Cornish, Crevecoeur, Cubalaya, Dutch, Hamburg, Japanese, Java, Jersey Giant, LaFleche, Langshan, Malay, Modern Game, Old English Game, Orpington, Plymouth Rock, Rosecomb, Shamo, Sumatra, and Wyandotte (typically Partridge based). (4)

It is worth noting that is it possible to get black in these breeds without using melanotic, and not all of these bird with melanotic will appear solid, show quality black. There are also varieties outside of black that use the melanotic gene.

The mottling gene in chickens creates a pattern of white spangles across the tip of usually black feathers. It is a fairly common mutation, and the birds will exhibit more white across the feathers and more white-tipped feathers overall as the bird ages. It has also been suggested that the mottled gene is the same as the recessive pied gene in chickens.

It is completely recessive, meaning you will only see white spangling with two copies of the gene. It is often used in combination with other mutations to create varieties such as millie fleur (mahogany + colombian + mottled), speckled (wheaton + gold dilute + mahogany + mottled), and porcelain (mahogany + colombian + lavender + mottled).

The APA recognizes the following breeds with mottling: d'Anver, d'Uccle, Cochin (bantam), Cornish (bantam), Houdan, Japanese, and Java.

They also recognize the following breeds with millie fleur: Old English, and the following breeds with both porcelain and millie fleur: d'Anver, d'Uccle, and Booted. Spangled is an accepted variety for Aseel, Cornish, Malay, Old English, and Sussex are recognized for their speckled variety.

The beard and muff gene in chickens causes the bird to present feathers from the side of the head around to the bottom of the beak, creating a "beard" like look. The muff is defined as the feathers from the side of the head, and the beard is the feathers directly under the beak, though they are both controlled by the same gene. This mutation also causes the wattles on the bird to shrink somewhat and be covered by feathers.

In heterozygous form (one copy of Beard and Muff), the bird will just have a smaller beard and muff, with shorter feathers than the full bearded counterpart. The fuller beard is almost always preferred.

APA Recognized bearded Breeds include the Polish, Silkie, All of the Belgium Bantams, Favorelles, Ameraucana, Sultan, Crevecour, and Houdan.

The multiple spur gene causes chickens to grow at least two additional spurs on the hock - usually one above the central spur, and one below the central spur. This can be seen in hens, chicks, and cock birds, with hens and chicks showing three prominent scales instead of full spurs. Chickens can have as few as three spurs with this gene, or as many as five. It works in tandem with the recessive spur gene.

The only recognized breeds in the APA to have multiple spurs are the Sumatra and Cubalaya.

The naked neck gene in chickens stops the bird from growing feathers in the neck (and sometimes vent), giving it a plucked or naked look to the upper portion of the bird. There will usually be some feather growth on the top of the head, and then bare skin down to the beginning of the breast.

In heterozygous form, or with only one copy of the gene, the bird will have a "bowtie" look of several feathers grouped together at the bottom of the neck, which isn't seen in homozygous form (with two copies of the gene).

The APA recognizes the Naked Neck (also called Turken) as its own breed in both largefowl and bantam.

The pattern gene (Pg) in chickens is crucial for creating specific feather patterns like lacing and penciling. This gene organizes the black pigment in a concentric pattern around the feather, contributing to the distinctive lacing effect seen in some breeds. Research has shown that the Pg gene works in conjunction with other genes, such as the melanotic gene (Ml) and the columbian gene (Co), to produce these patterns. The pattern gene by itself isn't noticeable without these other genes.

For example, the melanotic gene enhances and moves black pigment to the feather's edge, while the columbian gene restricts eumelanin in the center of the feather, leading to single lacing. When both the pattern and melanosis genes are present, you get double lacing patterns. The pattern gene is also responsible for enhancing autosomal barring, partridge, penciling, and other varieties.

The gene is most often seen in homozygous form (two copies of the gene) for lacing, penciling, and other varieties. In heterozygous form (one copy of the gene), the lacing and overall pattern will be much less refined and complete, and smut is more common.

The APA recognizes golden and silver laced in cochins, wyandottes, and sebrights. In bantam Cornish, white laced red and blue laced red are also accepted. Polish is the only breed with the chamois accepted, or buff laced with white. Wyandottes, Hamburgs, and Rocks are recognized in the silver penciled variety. The gold penciling is only recognized in Hamburgs. Brahmas and Campines are breeds that also utilize the pattern gene for different varieties.

The pea comb gene creates a shorter comb on the top of the head, similiar rose comb, though slightly taller with three ridges through the center. It is dominant, so a bird will have the typical "pea comb" look regardless of it is has one copy of the gene or two.

The pea comb gene also works with other genes to create the walnut and cushion comb. The walnut comb is at least one copy of the pea comb gene plus at least one copy of the rose comb gene. The cushion comb is a walnut comb (pea gene + rose comb gene) plus a smoothing gene.

APA recognized pea comb breeds include: Ameraucana, Araucana, Aseel, Brahma, Buckeye, Cornish, Cubalaya, Shamo, Sumatra, and Yokohama

Polydactyly is a mutation in chickens and ducks that causes the bird to grow an extra toe on the backside of the foot, near the hind-facing fourth toe. There are two different genes responsible for the toe depending on the heritage of the chicken - Asiatic breeds have a different gene then the European breeds do, but both genes act in the same way. The same gene is also seen in mice, cattle, pigs, cats, and humans.

It is a dominant gene, meaning the chicken will have an extra toe regardless of it only has one or two copies of the gene. There is a separate mutation that causes a partial fifth toe to grow from the same stem of the fourth toe that can crop up in polydactyly breedings, but this isn't related.

Dorkings (European), Hamburgs (European), Chinese You (Asiatic), Favorelles (European), Silkies (Asiatic), all have the polydactyly gene.

The foot feathering gene in chickens and pigeons, scientifically called Ptilopody and caused from multiple mutations, makes the bird grow various amounts of feathers from the hock, down through the shank, and sometimes across the foot. This gene has been thought to link chickens to dinosaurs and help shape our knowledge of evolution in general.

The amount of feathering varies from species and breeds, and is mostly due to selective breeding. Some breeds, such as the Marans, require feathering just down the shank, while other breeds like the cochin require feathers across the foot through at least the middle toe. Patterning of the feathers is dependent on the variety.

APA recognized breeds with feathered feet include d'Uccle, Booted Bantams, Brahma, Cochin, Favorelles, Langshan, Silkie, Sultan, and Marans.

Recessive white is a gene commonly seen in certain white varieties, most notably Rocks. It causes the bird to be entirely white and covers up almost all other colors and mutations, though chicks may have a slight red tinge to the plumage.

Where dominant white affects only the black plumage (eumelanin) and not gold (pheomelanin), the recessive white gene affects both eumelanin and pheomelanin, making it much less likely to get smuttiness, black feathers, or brassiness that can creep in with dominant white. Therefore, it is often used to create the white varieties found in the showroom, aside from most leghorn lines.

The APA recognizes white in either dominant or recessive form in the following breeds: Ameraucana, American Game, Araucana, Aseel, d'Anver, d'Uccle, Booted Bantam, Chantecler, Cochin, Cubalaya, Dorking, Cornish, Favorelles, Hamburg, Holland, Houdan, Japanese, Jersey Giant, Lamona, Langshan, Leghorn (typically dominant white), Malay, Marans, Minorca, Modern Game, Naked Neck, Old English, Orpington, Plymouth Rock, Polish, Rhode Island White, Rosecomb, Serama, Silkie, Spanish, Sultan, Wyandotte and Yokohama.

Rose Comb causes the normal single comb to flatten out and widen through the head. It has a low, rounded profile unlike the pea comb gene, and has a distinct spike, called a leader, that comes from the back of the comb and either lays flat on the head or extends a bit upwards. It is typically bumpy in texture, though there is a separate smoothing gene that causes the comb to be smooth and flat across the top. Typically this smooth look is desired.

There are two identical strains of rosecomb, one noted to cause fertility issues, and a second on a close allele that does not cause any fertility issues.

Rose comb also works with the pea comb and a possible smoothing gene to create the walnut and cushion comb.

Sex-linked silver is gene that turns the pheomelanin (red tones) in a chicken to almost entirely white. It is arguably one of the most researched and utilized genes in poultry due to the use in the hatchery, meat, and egg production industries.

Silver is used in many different breeds and varieties. On wildtype males (often called silver duckwing), the silver gene will make the hackle, saddle, wings, and flight feathers, but retain a black breast. The main tail feathers will be a green, with a green bar across the wings. In females, the color is a bit more diverse. They will have white hackles, grey patterned wings and cape, black tail, and a red breast.

Other recognized patterns include silver laced, silver pencilled, silver spangled, silver blue, and fawn silver duckwing. It also is used with dominant white to try and prevent gold and red leakage. In general, silver will replace any naturally red pattern with a light grey or white color.

The APA recognizes silver duckwing in American Game, Araucana, Modern Game, and Old English Game.
Silver is a recognized variety in Ameraucana, Campine (with the autosomal barring gene), Polish, Leghorn, Dutch, Phoenix, and Sebright (with the pattern and colombian gene), and Dorking.

Delaware, Rhode Island White, Leghorn, Hamburg, Cornish, and other recognized breeds also naturally have silver.

The silkie gene in chickens causes the feathers to be a silky, floofy texture similar to chick down. The "look" is created from the feathers having long barbs and lacking the "scroll" portion of the feather that keeps the barbs together.

It is a recessive gene, so both parents need to have at least one copy of the gene for any chicks to show silkie feathering.

It is only recognized by the APA for the Silkie chicken breed, though the mutation can also be found in Seramas.

The smoothing gene is a proposed gene by the author used to explain the differences in rose comb phenotypes. It is unknown and untested, though. The following is a theory currently being tested by the author.

The smoothing gene would be responsible for creating the flat rose comb seen on Wyandottes and a few other breeds. It would also likely play a role in the strawberry and walnut comb seen in several chicken breeds, compared to the typical cushion comb.

Split wing, or a gene that causes the absence of the axial feather on one or both of the wings in poultry is an under-researched mutation in the industry. It is believed by breeders to have a simple autosomal recessive inheritance, making it hard to breed out of flocks, but has not been confirmed in a lab.

The axial feather itself is crucial to the structural development of the wing, as one of the first parts of the wing to develop on the embryo. It is important enough that the APA considers almost all split wing to be a disqualification.

Interestingly enough, it has been shown that having two copies of split wing increases the overall growth and carcass traits of broilers in the Asian tropics. This may be the reasoning behind some breeds requiring the split wing.

The APA only recognizes split wing in the Ko Shamo and Aseel, though it is naturally found in the O Shamo and Nankin Shamo as well. It is considered a disqualification in all other breeds.

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The ear tuft gene creates a group of feathers that stick out sideways from the chicken's head near the ear canal. It is not the same mutation that causes beards or muffs in Ameruacanas and a few other chicken breeds. It is lethal in homozygous form, and almost all embroyos will die in the shell at about day 17. In heterozygous form, it still can lead to low hatch rates and trouble hatching.

Despite the high mortality rate, it is still common in some breeds of chicken, most notably the Araucana fowl, the Quetros, and other lesser known breeds.

Araucanas are the only breed recognized by the APA.

Vulture hocks are a gene found in both pigeons and chickens that causes the feathering down the thigh and shank to come to a point well past the hock. It is likely correlated to the ptilopody (foot feathering) gene, but is not the same. Not all breeds with the foot feathering gene have vulture hocks, but all bird with vulture hocks are ptilopodyl.

While it is not believed to cause any health or growth issues in poultry, it is only recognized in certain breeds for aesthetic purposes. It also is linked to possible musculoskeletal development from dinosaurs.

The APA requires vulture hocks in the Booted Bantam, d'Uccles, and Sultan. It is also naturally found in the unrecognized Breda fowl and both the rare Ispemic and Bulgarian Dzhinka breeds. It is considered an extreme defect to the point of being a disqualification in all other breeds.

The wheaten gene in chickens is characterized by a range of colors from creamy white to yellowish-white, salmon, or pale tan. This pattern is similar in palette to ripe wheat heads, hence the name "wheaten."

Males will often be darker, with a black breast and bright reddish orange saddle and hackles, while females will be a pale tan with the same reddish head color. Black primaries and tail feathers are common.

The APA currently recognizes wheaten as an acceptable variety in Malays, Shamo (Ko and O), Ameraucana, Aseel, Japanese Bantam, Marans, Modern Game, and Old English Game. It is also naturally found in the Favorelles and New Hampshires.

The yellow skin gene in chickens most notably