These bizzare photographs are those of a breed of chicken found in Australia known locally as a 'Turken'. They have almost no feathers on the neck and have a reduction in the number of feather tracts on other parts of their body. This unusual strain of naked neck has a pea comb and lays blue or green shelled egg. In the world of show poultry the name Turken is given to a breed that has a single comb and lays a brown shelled egg. Naked necks are also called a Turkens because the loose red skin on the neck resembles that of a turkey
A pea comb is a three bladed comb, with the blades side by side and the central blade a little higher than the lateral blades. This type of comb resembles an opened pea comb and hence the name for this comb type.
The picture on the left is that of a rooster and the one on the right is a hen. Both sexes have a pea comb and a naked neck, the female lays blue or green shelled eggs and the male carries the gene for blue egg shell colour. The naked neck trait is derived from the Transylvanian naked neck breed and the pea comb and blue egg traits are derived from the Araucana breed from South America. The blue shell colour does not affect the content of the eggs which is no different to the whites or yolks of white or brown eggs.
The naked neck condition, the pea comb and the blue egg shell traits are under the control of genes. In fact these traits are all controlled by dominant genes. Poultry geneticists use upper case O to represent the gene for the blue egg shell trait, upper case P to represent the gene for a pea comb and upper case Na to represent the gene for a naked neck. The recessive genes are represented by lower case letters so the brown or white shell gene is represented by an o, the single comb gene by a p and the fully feathered gene by an na. Poultry, like most living things, carry at least two genes for every trait. An individual that carries two of the same genes is said to be homozygous and an individual that carries one of each type of gene is said to be heterozygous . A bird that has two blue shell genes (OO) or two white shell genes (oo) are said to be homozygous and those carrying a blue and a white shell gene (Oo) are said to be heterozygous. The three genes are all located on the same chromosome - chromosome 1.
The chromosome map above shows the order of the genes on chromosome 1. The blue egg and pea comb genes are so closely linked that they are generally inherited together. A bird which has a pea comb will nearly always lay a blue shelled egg if it is a hen or pass the traits to its offspring if it is a rooster. The naked neck gene and silkie genes are further down the chromosome.
There are suggestions that the Turken arose out of a cross between a Brush Turkey and an Araucana but this is not possible given that they are two different species with different chromosome numbers. The more plausible explanation is a chromosomal re-arrangement that took place in a Transylvanian Naked Neck-Araucana hybrid which resulted in all three genes being positioned on the same chromosome. I have crossed the Turken with a number of bantam breeds and found the offspring are all fertile. Turken hens are interesting in that they have virtually no wattles or comb. I have found two types of pea combs in the Turken which can be selected for when breeding. One type has a small pea comb as seen in the red coloured hen shown in the left picture and the other has a different form of the pea comb which I call a bulbous comb as seen in the rooster on the right. Hens with the bulbous form of the pea comb have no comb at all but flat red skin where the comb should be. This is difficult to see in the picture of the hen on the top of the page.
I have used the the Turken to introduce the blue egg shell gene into the Chinese Silkie breed. This was done by crossing a turken hen with a Silkie rooster and then back crossing the naked neck blue egg laying silkie hens produced each year with unrelated Silkie roosters.This backcrossing has been done for 10 generations. I was fortunate in that the original Turken hen was also carrying the Silkie gene (h) located on the same chromosome as the blue shell, pea comb, and naked neck genes.The chromosome map at the top of the page shows the position of the silkie gene with respect to the other genes on the chromosome.
The naked neck blue egg laying Silkies have blue-black skin on the neck and breast and their turquoise blue ear lobes are exposed by the naked neck trait. This effect is accentuated in white feathered birds.
The picture on the left is that of a naked neck blue egg laying Silkie hen and the picture on the right is that of a naked neck Silkie cockrel (which carries the blue egg gene). The cockrel has very small wattles indicating that it is carrying the pea comb gene linked to the blue egg gene.
A cross between a blue egg laying naked neck Silkie
hen and a normal Silkie rooster also produces fully feathered Silkie hens
laying blue eggs.The fully feathered Silkie hen, whose picture appears
below, has all the characteristics required by the British and American
standards but it lays a blue egg. The eggs laid by Silkies carrying the
blue egg gene come in a range of shades- from a very light blue to a deep
olive green. Black silkie hens tends to lay dark olive green eggs. Silkie
eggs generally have a shiny appearance due to the waxy cuticle on the outside
of the shell. This cuticle is also present in the blue eggs.
I am currently developing a frizzle blue egg laying
Silkie ( I already have produced a frizzle silkie) and a bearded blue egg
My breeding program has shown that the standard Silkie shown in Australia does not have a true walnut comb as required by the British and American standards but in fact has a rose comb. The blue egg laying Silkies have a true walnut comb as they carry pea comb gene linked to the blue egg gene. The Silkie rooster on the left has a rose comb and the one on the right (which carries the blue egg gene) a true walnut comb.
The eggs below have all been laid by blue egg
laying Chinese Silkies. They come in a range of shades of blue, green and
olive. I have included a white and two chocolate brown eggs for comparison
Comb type in poultry is controlled by two pairs of genes. They are the rose loci and the pea loci where P represents the gene for a rose comb and p the gene for single comb and P the gene for pea comb and p the gene for single comb. A single comb bird will carry the following genes (rrpp), a rose comb bird will carry (RRpp or Rrpp) a pea combed bird will carry (rrPP or rrPp) and a walnut combed bird will carry (RRPP or RrPP or RRPp or RrPp). If a bird carries at least one rose comb gene and one pea comb gene( R_P_) it will have a walnut comb.
Further evidence to support the view that Australian Silkies (and possibly those shown overseas) are rose comb (R_pp) and not true walnut comb is provided by the size of the wattles and the absence of a breast ridge in our Silkies. Birds carrying two copies of the pea comb gene (PP) have very small wattles, birds carrying one copy of the pea comb gene (Pp) have a significant reduction in their wattle size and birds not carrying the pea comb gene (pp) have wattles that are normal in size. All Silkies I have seen in Australia, particularly the males have what I would describe as normal size wattles so they must be (pp) and cannot be walnut combed as they require at least one copy of the pea comb gene to display this trait. They are therefore rose combed (RRpp).
It has been established by Crawford (1961) that
the pea comb gene also produced what is called a breast ridge- a thickening
of the skin that runs down the keel of the bird. The picture below shows
a breast ridge in an Old English Bantam carrying the pea comb gene. This
ridge is missing in Silkies I have examined confirming they do not carry
the pea comb gene and are not walnut combed.
The blue egg laying Silkies I have developed do in fact carry the pea comb gene and the blue egg gene linked to that pea comb, they have a true walnut comb, they have smaller wattles confirming the presence of the pea comb gene and they also have a breast ridge. Not only has the breeding program introduced two new traits into the Chinese Silkie, the blue egg shell trait and the naked neck trait but it has also produced a comb that is true to the standard.
This naked neck Silkie rooster has a true walnut comb and a reduction in the size of the wattles.
If you would like more information I can be contacted on firstname.lastname@example.org . If you would like to view an article I wrote for the Australian Poultry Science Symposium (1999) "The Genetic Basis of the Introduction of the Blue Egg Gene into the Chinese Silkie"
updated 1 Feb 1999