Written by the Sellers family of Brookings, South Dakota

The third part of this series - if you haven't already, please read the first part and the second part to cover the basics and get you to this level

Below is a table of genes and gene symbols. Allelic genes (genes that have the same location or locus on a chromosome, which are also genes that substitute for one another) are grouped together. I have tried to incorporate relevant and interesting comments about these genes in the comment section. I continue to update this and correct it....

Sex-Linked Genes (alleles)	Symbol	Comments
Sex-linked barring	B	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.
	b+	Recessive wild-type gene. An allele of the sex-linked barring locus. Lack of barring.
Sex-linked dilution	BSd	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.
comments		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	br	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.
Dwarf	dw	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%.
	dwB	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.
	dwM	MacDonald dwarf. Reduces body weight by 13.5% and shank length by 9%. Allelic with dw.
	Dw+	Wild-type gene. Lack of dwarfing alleles. Allows 'normal' size to develop.
Silver and Red-Gold	S	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.
	s+	This gene is sometimes called 'gold'. Wild-type, recessive. Invokes red pigment.
Foot Color	Id	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
	idc	Recessive. This gene allows beak and sometimes plumage pigmentation in dominant white homozygotes.
	ida	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.
	idM	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.
	id+	Wild-type dermal melanin. Lack of dermal melanin inhibitors.
Sex-linked white skin	y	Recessive, causes white skin. Recessive sex-linked white skin causes yolks to be lighter in color and reduces xanthophyll levels in blood plasma. This is generally considered to be an inferior trait particularly since the autosomal white skin does not have these side effects on yolk color.
	Y+	Wild-type gene. Lack of recessive white skin mutation.
Feathering Rate Genes	k+	Sometimes called rapid feathering. Recessive.
	K	Late feathering gene
	Ks	Slow feathering gene
	Kn	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	pr	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 Genes	Symbol	Comments
Creeper	Cp	Short legged condition. Lethal in homozygous state. Dominant.
	cp+	Recessive, wild-type gene. Lack of creeper trait.
Rose comb	R	Associated with poor fertility in some homozygous breeds. Dominant.
	r+	Wild-type gene. Recessive. Lack of rose comb trait.
Lavender	lav	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.
	Lav+	Dominant, wild-type gene. Lack of lavender trait.

Autosomal Genes	Symbol	Comments
Crest	Cr	Crest feathers are similar in shape and texture to hackle feathers. There may be more than one allele. Incompletely dominant.
	cr+	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.
	Mo+	Wild-type gene. Dominant. Lack of mottling.
Dominant white	I	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.
Smoky	IS	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.
	ID	This gene is often called 'Dun'. Incompletely dominant, off-white. Allelic with dominant white.
	i+	Wild-type gene. Lack of dominant white.
Frizzle	F	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.
	f+	Recessive, wild-type gene. Lack of frizzle.

Autosomal Genes	Symbol	Comments
Skin Color	w	Yellow skin color. Recessive.
	W+	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	O	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.
	o	Recessive wild-type gene. Lack of blue eggshell color gene. Causes white eggshells in the absence of brown eggshell color genes.
Pea comb	P	Dominant. Sometimes referred to as triple comb. Heterozygotes often display a prominant central ridge with much smaller lateral points.
	p+	Wild-type gene. Recessive. Lack of pea comb.
Naked neck	Na	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.
	na+	Recessive, wild-type gene. Lack of naked neck. Allows full feathering.
Silkie	h	Recessive. The barbs of the feathers are highly modified giving the silkie a 'woolly appearance.
	H+	Dominant, wild-type gene. Lack of silkie trait. Allows normal feather structure.
Melanotic	Ml	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.
	ml+	Recessive, wild-type gene. Lack of melanotic eumelanin enhancing gene.
Pattern gene	Pg	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.
	pg+	Recessive. Wild-type gene. Lack of pattern gene.
Dark brown	Db	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.
	db+	Wild-type gene. Recessive. Lack of dark brown-type Columbian restriction.

Autosomal Genes	Symbol	Comments
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.
	d+	Recessive, wild-type gene. Lack of duplex trait.
Multiple spurs	M	Dominant. Causes more than one spur per shank on males.
	m+	Wild-type gene. Recessive. Lack of multiple spur trait.
Polydactyly	Po	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.
	Pod	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.
	po+	Wild-type, recessive. Allows normal foot.

on the next we look at other autosomal genes and then describe some of the terms used on these pages

 

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