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