Chicken Genes of Common Interest

Sex-Linked Genes (alleles)



Sex-linked barring


Barring, cuckoo barring. Dominant. Causes white barring pattern in red and black, sometimes used as a black inhibitor, most notably in Leghorns. Cuckoo barring is also an inhibitor of tissue pigmentation and is responsible for the yellow shanks of Barred Rocks. Shanks of females can be darker. Barring shows a distinct dosage effect. B/B gives wider bars than heterozygotes have. Incorporation of the slow feathering gene results in a cleaner, more sharply defined barring.


Recessive wild-type gene. An allele of the sex-linked barring locus. Lack of barring.

Sex-linked dilution


Females that are hemizygous for BSd (having one BSd gene) have light blue and barred plumage as do the heterozygous males, however, homozygous males show a dosage effect and are essentially white. These homozygous males resemble dominant whites but differ in that they are epistatic to pheomelanin while dominant white is not.


Sex-linked barring, B, sex-linked dilution, BSd and the wild-type, b+ are alleles of the same locus. The order of dominance is BSd > B > b+.

Brown eye


Not much is known about this gene and there may be a dominant inhibitor of brown eye. Many of the melanin-influencing genes have an effect on eye color.



Recessive. Males are reduced in size by about 43%, females by 26-32%. Multiple alleles have been proposed. dw is responsible for some beneficial effects. dw homozygotes are more resistant to Marek's Disease and spirochetosis, fewer laying accidents, more aggressive immune response. Abnormal eggs are suppressed (soft-shelled, double yolks). Dwarfism, dw, does not effect mortality but does postpone the onset of lay in pullets up to two weeks. Although egg number and mass are slightly decreased by dw, feed efficiency (feed consumption per egg layed) in laying stocks is usually increased 13-25%.


Recessive but shows a dose effect; 'bantam' gene. Females reduced in size by 5-11% and males by about 5% in heterozygotes and 14% in homozygotes. Allelic with dw.


MacDonald dwarf. Reduces body weight by 13.5% and shank length by 9%. Allelic with dw.




Wild-type gene. Lack of dwarfing alleles. Allows 'normal' size to develop.



Silver and Red-Gold


This gene is called 'silver'. Inhibits red pigment, pheomelanin. The expression of silver is sometimes affected by hormonal levels and is considered to be incompletely dominant and highly influenced by modifying genes.


This gene is sometimes called 'gold'. Wild-type, recessive. Invokes red pigment.

Foot Color


Light foot color. Dominant. Inhibits dermal melanin. Reported to have little influence on shank/foot color in birds with dark shanks due to E/E


Recessive. This gene allows beak and sometimes plumage pigmentation in dominant white homozygotes.


Allows green spots on shanks - this gene is not widely accepted and the effect of this gene may be due to the interaction of modifiers not allelic to this locus.


Massachusetts mutation. Recessive. Unlike other alleles that belong to this locus, dermal melanin is present in shanks of day-old chicks. Other alleles take more time to express. The darkest shanks are produced in conjunction with E and i+. The combination of idM, E and I produces a pale blue or green color by about three months of age.


Wild-type dermal melanin. Lack of dermal melanin inhibitors.

Sexlink white kin


Recessive, causes white skin.


Wild-type gene. Lack of recessive white skin mutation.

Feathering Rate Genes


Sometimes called rapid feathering. Recessive.


Late feathering gene


Slow feathering gene


Very slow feathering or 'delayed' feathering gene. The order of dominance among the genes allelic to this locus is Kn>Ks>K>k+. The slow feathering gene is believed to be associated with a bald patch on the back of the adolescent bird. The feathers do come in given enough time. Since this is likely due to a dose effect of the slow feathering gene, the homozygous males should be the most likely to exhibit the trait. In my personal flocks, I have both males and females exhibiting this. Many novice poultry keepers wrongly attribute the bald back phenotype with a picking problem.

Brown eggshell color inhibitor


This recessive gene results in a lack of protoporphyrin pigment (the brown eggshell pigment) even in hens with polygenic brown eggshell color. It can be employed to remove undesirable tints from eggs of white shelled strains.


Autosomal Linkage Group 1 Genes

Autosomal Genes





Short legged condition. Lethal in homozygous state. Dominant.


Recessive, wild-type gene. Lack of creeper trait.

Rose comb


Associated with poor fertility in some homozygous breeds. Dominant.


Wild-type gene. Recessive. Lack of rose comb trait.



Recessive lavender has been associated with poor feather quality and even lack of feathers in some breeds. Lavender dilutes both black and red; changes black to grey and red to cream. Blue fowls termed "self blue" are normally lavender homozygotes. A mating of two lav homozygotes (blue fowls) will produce blue offspring. Lavender causes dilution by inhibiting the transfer of pigment granules from melanocytes, which produce them, to the feather structure. Lavender expression in homozygotes is present in chicks and adults.


Dominant, wild-type gene. Lack of lavender trait.


Autosomal Linkage Group 2 Genes

Autosomal Genes





Crest feathers are similar in shape and texture to hackle feathers. There may be more than one allele. Incompletely dominant.


Wild-type gene. Lack of crest.

Pied / Mottle

mo (pi)

The pied pattern is recessive black and white as in Exchequer Leghorn. Research has shown that the pied and mottle patterns are due to the mottle gene. It is no longer accepted that 'pied' is a distinct gene from mottle, however it is not known why the mottle gene causes the pied pattern in some birds and the typical mottle pattern in others. Mottle causes a white tip at the distal end (end farthest from the skin) of the feather. Chicks with extended black and mottle (E/E mo/mo) as in the Exchequer Leghorn will often have black restricted from the belly and sometimes the head.


Wild-type gene. Dominant. Lack of mottling.

Dominant white


Incompletely dominant. Influences eye pigment. Inhibits black pigment, eumalanin. This gene is ‘leaky’ and will allow black specks through. Generally not as efficient at producing a solid white bird as are two copies of recessive white. Heterozygotes of dominant white, I/i+ are often grey with the grey color visible in the chick down. Dominant white dilutes, but does not eliminate, epidermal melanin.



The smoky gene is an allele belonging to the dominant white locus. Smoky is dominant to dominant white in both chick down and adult plumage in that extended black with I/IS (E/E I/IS)results in grey chick down and adult plumage. Research to date indicates that i+/IS heterozygotes express more the wild-type phenotype with respect to this gene indicating a recessive character with respect to the wild-type. Smoky is dominant on the chick down of IS/i+ heterozygotes in that down that should be black is grey. The melanosomes resulting from the expression of smoky resemble those resulting from Andalusian Blue. Smoky dilutes black much more than red/gold. An important difference between Smoky and Andalusian Blue is that Smoky in the homozygote state produces a grey/blue bird while Andalusian Blue homozygotes are splash. Therefore, Smoky fowl will breed true.


This gene is often called 'Dun'. Incompletely dominant, off-white. Allelic with dominant white.


Wild-type gene. Lack of dominant white.



Incompletely dominant. The action of the frizzle gene is localized in the feather follicle. It causes a structure abnormality in the feather and abnormalities of internal organs (enlarged heart, spleen, gizzard and alimentary canal) are common.


Recessive, wild-type gene. Lack of frizzle.


Autosomal Linkage Group 3 Genes

Autosomal Genes



Skin Color


Yellow skin color. Recessive.


Dominant wild-type gene. Autosomal white skin gene. Prevents the transfer of xanthophyll into the skin, beak and shanks but does not effect the eye iris, egg yolk or blood serum. This gene is considered to be the wild-type because it is present in the Jungle Fowl.

Blue eggshell


The action of the blue eggshell gene is dominant to the action of the white eggshell gene, o. Blue and brown egghell genes present simultaneously give a shade of green on the exterior of the egg. The blue eggshell color permeates the shell while brown is primarily an exterior coating.


Recessive wild-type gene. Lack of blue eggshell color gene. Causes white eggshells in the absence of brown eggshell color genes.

Pea comb


Dominant. Sometimes referred to as triple comb. Heterozygotes often display a prominant central ridge with much smaller lateral points.


Wild-type gene. Recessive. Lack of pea comb.

Naked neck


Incompletely dominant. Turkens. Causes bare skin on the neck which becomes reddish toward sexual maturity. Heterozygotes show a small tuft of feathers on the neck above the crop, which is almost missing in the homozygote. The Na allele is associated with increased tolerance for heat, which is probably due to the 30% reduction in overall plumage for heterozygotes and 40% for homozygotes. Na is also associated with a small increase in meat yield and lower body fat content. An increase in embryonic mortality of up to 10% is attributed to Na.


Recessive, wild-type gene. Lack of naked neck. Allows full feathering.



Recessive. The barbs of the feathers are highly modified giving the silkie a 'woolly appearance.


Dominant, wild-type gene. Lack of silkie trait. Allows normal feather structure.



Dominant. Black intensifyer, one of the genes which, in concert with Pg and other genes, is responsible for plumage patterns. There is speculation that there may be more than one eumelanin intensifying gene similar to Ml and non-allelic.


Recessive, wild-type gene. Lack of melanotic eumelanin enhancing gene.

Pattern gene


Dominant. This is the pattern gene which, together with other genes is responsible for the patterns of plumage. The pattern gene doesn’t seem to express in the absence of Ml in combination with some of the E locus alleles. See text. The pattern gene with the Db and Co Columbian-like restrictors is believed to be responsible for autosomal barring.


Recessive. Wild-type gene. Lack of pattern gene.

Dark brown


Incompletely dominant. Changes black down of E, ER to reddish-brown. Adults males exhibit a Columbian-type pattern of black, modifies red to orange-tan. Db is a better restrictor of black in males than females.


Wild-type gene. Recessive. Lack of dark brown-type Columbian restriction.


Autosomal Linkage Group 4 Genes

Autosomal Genes



Duplex comb

Dv, Dc

Dominant alleles. The superscripts 'v' and 'c' indicate the 'V' and 'cup' shaped phenotypes and are considered to be separate genes.


Recessive, wild-type gene. Lack of duplex trait.

Multiple spurs


Dominant. Causes more than one spur per shank on males.


Wild-type gene. Recessive. Lack of multiple spur trait.



Dominant. Having too many toes. The fifth toe develops on top of the first toe and is longer than the first toe. There are several degrees of expression of this gene.


Duplicate polydactyly. Dominant to the wild-type allele. An extra toe is present as well as an elogation and splitting of the original first toe. Extreme expression can accompany this gene in which the most extreme cases the entire foot is duplicated.


Wild-type, recessive. Allows normal foot.


Other Autosomal Genes

Autosomal Genes



Autosomal barring


Non-sex-linked barring. Sometimes called 'parallel pencilling'. This is not a real gene, rather autosomal barring is due to combinations of Pg, Co, Db with eb, ER, and ebc. See text.

Breda combless


Recessive. Birds with this gene are almost completely lacking comb and wattles. Females are considered to be completely combles and males have a tiny comb.


Dominant, wild-type gene. Lack of breda combless trait. It is believed that this gene is necessary for chickens to produce a comb.



Incompletely dominant. Andalusian blue-dilutes black: blue pigment is a modified black. Two nigrum genes, E, and one Bl gives a blue chicken; two Bl genes gives splash.


Wild-type gene. Recessive. Lack of blue eumelanin dilution gene, Bl.



Dominant. Abnormally short digits (toes).

Recessive white genes


Thought to give a cleaner white than dominant white. Varieties of White Plymouth Rock, Wyandotte, Minorca, Orpington, Jersey Giant, Dorking, Langshan, Silky and others often carry recessive white genes. Many varieties carry both dominant and recessive white. Allows dark eyes. Pigmentation in chick down varies.


Recessive white allele that allows red eyes.


Autosomal albinism. Alellic with the recessive white genes. Evident via lack of eye pigment. Some melanin present in chick down.


Wild-type gene. Dominant. Lack of recessive white mutations.

Comments about the C locus

The order of dominance among the recessive white alleles is: C+>c>cre>ca. The presence of other pigment inhibiting or enhancing genes will influence the chick down color. Some adults have a grey color.

Champagne blond


Dominant. Inhibits pheomelanin (red / gold). The presence of the gene is not observable on the wild-type down


Wild-type gene. Recessive. Lack of chanpagne blond dilution.



Incompletely dominant.Confines black to hackle and tail in both sexes (called Columbian restriction). Thought to cause a gradient in color from head to tail. Modifies Wheaten to Buff Columbian. Has no effect on extended black, E.


Wild-type gene. Lack of Columbian restriction. Recessive.

Red diluter


Dominant. Dilutes red, changes red to buff.


Wild-type gene. Lack of red diluter. Recessive.



A proposed gene of an allelemorphic series that darkens the shade of red. Pheomelanin enhancer(s). Dkl was proposed for the dark brown Leghorn and dk+ for the wild-type allele.



This gene may be Columbian, Co, or closely related. This may not be a distinct gene.


no symbol

Recessive, dilutes black to brown/grey.

The E-locus alleles


Often called 'extended black', 'nigrum' or 'self black'. Extends black, changes red to black, red inhibitor.


Birchen. Resembles extended black, E, but with non-black breaks on head and hackle. Body is black with some stippling (flecks/dots) of other color. Used as red inhibitor in Leghorn.


Partridge (brown). Sometimes represented as ep, females have non-salmon breast with stippling. Males are wild-type.


Dominant wheaten. Female body varies from light salmon to wheat color, some black may be present. Males are wild-type.


Wild-type. Female: breast is salmon brown and devoid of stippling, body is black and brown in stippled pattern. Males: black breast and abdomen; non-black hackle, saddle and wings.


Speckled. Resembles eb but with less pronounced stippling. Males are wild-type.


Recessive wheaten. Female: resembles dominant wheaten with more coarse black stippling on breast and back. Males are wild type.


Buttercup allele. Resembles the eb phenotype.

Comments on E-locus alleles

The order of dominance among the generally accepted E-locus alleles is: E>ER>e+>eb>es>ebc>ey. The birchen allele is incompletely dominant to dominant wheaten and the wild-type alleles. Additional alleles have been proposed for the E-locus but research to verify these as separate alleles has not been done. As of this writing, the buttercup allele has been sequenced and has been found to be the same sequence as the eb allele. The buttercup phenotype then is due to modifiers or interactions with other genes. Every E-locus allele influences adult female phenotype. However, all the adult male phenotypes are the same as wild-type except for extended black and birchen.

Ear tuft


Dominant. Lethal in homozygous state. Thought to be associated with birth defects, particularly in the ear structures.


Wild-type gene. Recessive. Lack of ear tufts.


no symbol

Black spots and flecks, variable black and white feathers, similar to pied.



Dominant. Sounds like a disease. The name was suggested by F. Hutt in the 1940s to emphasize the association with connective tissue pigmentation. This gene is responsible for the deep skin pigmentation of silkie. Fm is strongly influenced by dermal melanin inhibitors such as the sex-linked Id mutation.


Wild-type gene. Recessive. Lack of fibromelanosis.

Long tail

Gt, mt

The Gt gene (dominant) allows continual growth of tail and saddle feathers. The mt gene allows certain tail and saddle feathers to be nonmolting.

Henny plumage


Dominant. The term comes from 'hen feathering' in which male plumage is indistinguishable from female plumage.


Wild-type gene. Recessive. Lack of henny feathering.



Dilutes red. Recessive. A major pheomelanin dilution gene. The gene symbol derives from "inhibitor of gold".


Wild-type gene. Dominant. Lack of cream dilution.



This is not a real gene. See text. Partridge Rock, Silver Pencilled Rock.



Incompletely dominant. Characteristic of Ameraucana, Easter Egg Chickens (faux-Araucana)


Wild-type gene. Recessive. Lack of beard-muff.

frizzle modifyer


Recessive. Reduces/modifies the effect or expression of the frizzle gene. This gene can modify frizzle heterozygote expression to the point that they are almost indistinguishable from the wild type. Modifies the extreme expression of the frizzle homozygote.


Wild-type gene (uncertain). Dominant. Lack of frizzle modifyer.

Recessive melanotic


Enhances black, (helps) change red to black. E + mi gives a black chicken.


Wild-type gene. Dominant. Lack of recessive melanotic enhancing.



Recessive. Makes a white tip on end of feather. Changes a black bird to Mottled and a Buff Columbian to a Mille Fleur. Dilutes epidermal melanin. There may be several alleles corresponding to this locus or non-allelic modifying genes.


Wild-type gene. Dominant. Lack of mottling.



Dominant. Mahogany restricts eumelanin and enhances the color of red. Rhode Island Red is a good example. Restricts black in the back and wing of both males and females. Down color seemes to be unaffected by mahogany.


Wild-type gene. Recessive. Lack of mahogany.

Pink-eye dilute


Dilutes both feathers and eye color. Recessive.

Recessive polydactyly


Recessive. A number of extra toes can be present even ascending the shank. Associated with leg deformities, significant decrease in hatchability and much higher post-natal mortality.

Feathered legs

Pti-1, Pti-2

Dominant. Two different feathered leg genes. Research has shown that these genes are most likely not allelic (they belong to different loci of the chromosome). When both are present, heavy feathering as in Cochin, Sultan, Belgian d’Uccle. If only one is present, the feathering is weaker as in Langshan, Faverolle, Breda. Genes demonstrate a dose effect.

Recessive feathered legs


The recessive leg feathering gene was identified in a Russian breed referred to as the Pavlov breed. Test matings confirmed the recessive nature of this gene.

Dominant Rumplessness


No coccyx (tail vertebra), reduces hatchability.


Wild-type gene. Recessive. Lack of dominant rumplessness. Fowls usually have tails.

Recessive Rumplessness


A skeletal mutation commonly called 'roachback'.

Red spash white


Recessive. Two copies of this gene give a white bird with spashes of red and black. Chicks are white with a red head spot. This gene may be extinct now. It was first isolated in a line of Rhode Island Reds, but it was not maintained nor has it be re-identified.

Recessive black


Not much is known about this gene. Eumelanin intensifier. There may be a number of genes that play this role.



Recessive. Fowls have no spurs.

Snow-white down


Recessive. The chick down is white rather than yellow.

Vulture hocks


Recessive. Long and stiff feathers on the posterior area of the tibia. Characteristic of Belgian Bearded d'Uccle, Breda, Sultan.

Dorking white







Allele                One of a number of possible alternative forms of genetic information at a gene locus [1].  A member of a set of genes that all have the same location on a given chromosome.  For example, extended black and birchen are allelic genes ( to each other) because they are both found at the E locus or location.

Epistasis           (also epistacy) suppression of the effect of a gene by a nonallelic gene [3].  A gene for trait A somehow having an effect on triat B is an example of  epistasis.

Gene                The unit of heredity [1]. A piece of DNA in a chromosome that contains the coded information for a trait.

Generation notation: The original members of a mating are referred to as the parental (P) generation.  The first generation of progeny from the parental cross is referred to as the first filial generation, F1.  The progeny of a cross in which one or both of the parents are from the F1 generation is an F2 generation (F1 x F1 = F2) and so on [1].

Heterosis          The deviation between the cross and midparent means [2].  The difference in some property, for example rate of lay, between a cross bred line and the average for the parent lines.  For example, “hybrid vigor” can be thought of as an effect of heterosis.


1.                     J.J. Pasternak, An Introduction to Human Molecular Genetics,         Mechanisms of Inherited Diseases, Fitzgerald Science Press, Bethesda,               MD 1999.

2.                     R.W. Fairfull in Poultry Breeding and Genetics, R.D. Crawford, ed., Elsevier, 1990, page 913.

3.                     Webster’s Seventh Collegiate Dictionary


Poultry Genome Project              

Poultry Genetics Board




A sex-linked chicken, quite simply, is a chicken whose sex is visible to the naked eye immediately after hatching. Usually male and female sex-linked chickens have markedly different colors or feather patterns. The

reason that this is desired is that most people want hens for egg-laying purposes, and roosters not only are not desired, but are even prohibited by local ordinance in some communities because of their loud crowing.

Sex-linked Chickens are Hybrids

In the first place, both red sex-link, also called Red Stars, and black sex-link chickens, also called Black Stars, are, by definition, hybrids. That means they are not true breeds unto themselves, but are the result of crossing a rooster of one breed and a hen of another breed in order to get off-spring with certain characteristics.They do not breed true in subsequent generations.

Sex-linked Wing Feathering Rates

There are several kinds of sex-linked chickens that are popularly sold by the big hatcheries. Red sex-links and black sex-links are the most popular. There is also a sex-linked gene that allows the wing feathers of male and female chicks to grow at different rates that can be used to determine whether day old chicks are male or female. The wing feathering genes can be used in certain breeds of pure-bred chickens for those that want their flocks to breed true, generation after generation. For a more in-depth catalog of wing feathering rate and other genes, the Sellers family maintains a
list of Chicken Genes of Common Interest.

Sex-linked Genes

In chickens, the female has one gene for sex and the male has two. The male gives a sex-link gene to all of its offspring, while a hen may give either one or none. Off-spring who received two sex genes (one from each parent) are males, while those receiving only a single sex link gene (from the rooster), are females. Therefore, any baby chick that receives a dominant color gene from its mother when crossed with a rooster whose breed has only recessive sex-linked color genes will exhibit the color dictated by the mother's dominant gene and will be a male. Others will exhibit color like the parent rooster and will have a single recessive color gene.

Sex-link Chicken Parent Breeds

Red sex-link chickens are a cross between a predominantly red rooster breed such as the New Hampshire Red which carries two recessive gold color genes, designated s+, and a hen which carries the Dominant Silver gene, designated S, such as a Delaware White. These are not the only two breeds used to create the red sex-linked hybrid; any that carry the appropriate sex-linked genes for color can be used. Any baby red sex-link chick who received the Silver gene and thus presents a yellow down and grows white feathers is necessarily a male. Female red sex-link chicks will have a reddish down and will grow red feathers because they do not carry a copy of the dominant Silver gene. As red sex-link roosters attain maturity, they will typically show some red patches on their backs, but will remain predominantly white. The same scenario holds for black sex-linked chickens. Except in this case, a New Hampshire Red or Rhode Island Red rooster is crossed with a Barred Rock hen. The male black sex-linked chicks, will be distinguishable by a white spot on the top of their heads. The males may also show a light barring pattern, while the females will not.

Hybrid Vigor in Sex-link Chickens

Hybrid chicken breeds like the sex-linked varieties often demonstrate hybrid vigor or heterosis. Hybrid vigor is defined by Gardner and Snustad in Principles of Genetics as "Unusual growth, strength, and health of heterozygous hybrids from two less vigorous homozygous parents." In other words, hybrid offspring may be bigger, stronger, and lay more eggs than the typical breed of either of the parents. This is another reason that hybrid breeds like the sex-linked chicken are widely used for egg production.

Sex-linked Chickens Do Not Breed True

The problem with both black and red sex-link chickens is that after the initial generation of hybrids, all the babies will no longer be sex-linked. The males are now heterozygotes, meaning they each have one Dominant Silver gene and one gold (red color) gene. Thus they will give fifty percent of the females a Silver gene and 50% a gold gene. The males will get a recessive red gene from the mother and either a Dominant Silver or a second recessive gold gene from the father. Therefore, both male and female chickens from the second generation of red-sex links will be half red chickens and half white chickens. The images attached to this article show Punnett Squares for first and second generation Red-sex Link chickens as well as a conversion of genotype to phenotype (appearance).

Third Generation of Sex-Links May Show Sex-Linked Color Again

Looking at the second generation Punnett Square, however, we can see that red males of this generation are once again homozygotes for recessive red color genes. Similarly, White females of this generation possess only the dominant Silver gene. Using these portions of the 2nd generation, one could again achieve sex-linked coloration in third generation chicks using just this portion of the second generation population. Other traits would not fall in line with the sex-linked coloring, so hybrid vigor would not necessarily be present.


Sellers family. Chicken genes of common interest. Retrieved from on March 2nd, 2010.

Gardner, Eldon J., and Snustad, D. Peter. 1984. Principles of Genetics, Seventh Edition. John Wiley & Sons, Inc., New York.