Brown Egg Blue Egg

Willow Legs

 

By Alan Stanford, Ph.D.

Brown Egg Blue Egg

 

The American Poultry Association's 1998 American Standard of Perfection calls for willow legs on black, black breasted red, golden duckwing, and silver duckwing Araucanas.   It describes willow as the "dusky yellowish green color found on the shanks, feet and toes of some breeds and varieties of fowl."

 

Genes at two different loci create willow legs.   A locus (plural loci) is the position of a gene on a chromosome.   Genes at one locus determine the color of the deep layers of skin on the shanks, feet, and toes.   Genes at another locus control the color of the outer.   The shanks, feet, and toes of willow legged birds have

 

yellow deep layers of skin and

dark outer layers of skin.  

 

The deep layers of skin on the shanks, feet, and toes can be either yellow or white.   The locus for the deep layers can have either a dominant gene, W, for white legs

 

            W - white deep layers

 

Or a recessive gene, w, for yellow legs

 

            w - yellow deep layers.

 

The outer layers can have or not have dark pigments.   The locus that determines the outer layer's color can have either a sex linked recessive gene

 

id+ dermal melanin - dark pigments in the outer layers


or have a sex linked dominant gene

 

Id dermal melanin inhibitor - no dark pigments in the outer layers


Males have a locus for this sex linked gene on two matching chromosomes.   Females have only one locus for this sex linked gene.   In chickens the females are "heterogametic".   They have one chromosome that is much smaller than its partner chromosome.   Males have two of the large partner chromosomes.   The female sex chromosome is thought to be empty and equivalent to not having a chromosome.   In humans it is the male that has the small sex chromosome.  


Here are the possible gene combinations for birds that are homozygous for the w (yellow deep skin layers) gene.   Homozygous means the individual has the same gene at a particular locus; the same gene at the same spot on matching chromosomes.   Genotype is the genetic make up of an organism, and is different from the organism's physical appearance (its phenotype).  

  

Sex

Deep Skin Layer

Outer Skin Layer

Leg Color

Genotype

Phenotype

Genotype

Phenotype

Phenotype

Male

w,w

Yellow

Id,Id

Light

Yellow

Male

w,w

Yellow

Id,id+

Light

Yellow

Male

w,w

Yellow

id+,id+

Dark

Willow

Female

w,w

Yellow

Id,-

Light

Yellow

Female

w,w

Yellow

id+,-

Dark

Willow

Females are either pure for green leg or pure for the yellow leg because of sex linkage.   Males can have the desired id+ gene and yellow legs.   The find out if a male has the id+ gene, mate him with a willow legged female.   If all the chicks have yellow legs, that male does not have the id+ gene.   You need to hatch a good number of chicks to get an accurate genetic picture.

 

Glossary

1.       A locus (plural loci) is the position of a gene on a chromosome.  

2.       In chickens the females are "heterogametic".   They have one chromosome that is much smaller than its partner chromosome.   Males have two of the large partner chromosomes.   The female sex chromosome is thought to be empty and equivalent to not having a chromosome.   In humans it is the male that has one small sex chromosome.  

3.       Homozygous means the individual has the same gene at a particular locus; it has the same gene at the same spot on paired chromosomes.  

4.       Genotype is the genetic make up of an organism, and is different from the organism's physical appearance (its phenotype).



Brown Egg Blue Egg