Wednesday, February 26, 2014

The Expression of Autosomal Pheomelanin (Aph) and the Inhibitor of Autosomal Pheomelanin (Aph^I) on the common E-alleles (e+, eWh, eb, ER and E)

The Expression of Autosomal Pheomelanin (Aph) and the Inhibitor of Autosomal Pheomelanin (Aph^I) on the common E-alleles (e+, eWh, eb, ER and E)

Part 2 
Originally published October 2012 in Exhibition Poultry E-Zine


Brian Reeder

In this article, I will outline the effects of Autosomal pheomelanin and the Inhibitor of Autosomal pheomelanin on the five commonly encountered alleles of the e-locus.  It must be noted here, at the beginning of the article, that there are genes that interact with Aph and Aph^I beyond the e-alleles. Some of the most basic interaction factors were discussed in last month’s article ‘The Expression, Suppression and Interactions of Autosomal Pheomelanin (Aph) in the Domestic Fowl’, and include such factors as Mahogany, Dilute and cream. While this article will not deal with the other interaction genes (such as Columbian or Dark brown aka ‘ginger’), we will look at these factors in next month’s article. With that out of the way, let us continue on to discuss the e-locus interactions.

The five commonly seen e-alleles are e+ (duckwing), eb (brown), eWh (wheaten), ER (birchen) and E (extended black). Most simply stated, Autosomal pheomelanin is found on all of these alleles, though the distribution effect is somewhat different on each allele, most visibly on the females in several cases. The Inhibitor of Autosomal pheomelanin can also be found on, and express on, all of the e-alleles.

The males of all five e-alleles are much alike in their expression of Aph or Aph^I. There are subtle differences between the males of each allele that we will discuss below, but it is the females where Aph and/or Aph^I are often most visible and variable, and help to create the unique appearances that we most relate to the e-alleles.

As I stated in my article last month, I feel that Aph is found in all of the jungle fowls and that Aph^I is found in the gray jungle fowl and perhaps also in the green jungle fowl. Whether the form of Aph^I found in the gray jungle fowl is exactly the same as that found in the modern domestic fowl is not clear, but it is the likely source of Aph^I in the domestic fowl and if not the exact same gene is likely the precursor to Aph^I as described in domestic fowl, just as the yellow skin gene found in the gray jungle fowl is now thought to be the precursor to, and origin of, the yellow skin gene found in the domestic fowl.

The E-alleles
As we discuss the e-allele expressions of Aph and Aph^I, it is very important to bear in mind that I am discussing these alleles in their most basic expression. For example, E (extended black) is commonly thought of as a black chicken, but as I pointed out in my article two months ago on the genetics of black chickens, E, in and of itself, does not create a solid black chicken, and requires melanization factors to completely melanize an E-based bird to solid black. Thus, as I describe the interactions of E with Aph and Aph^I, I am discussing that allele without the extra modifiers. In other words, I am not discussing the melanized expression of E, the fully black bird, but am discussing the allele in its most basic state, where pheomelanin expresses in some parts. The same will be true for all of the other e-alleles. Our discussion for this article will be restricted to the e-allele with consideration of the s-allele and it’s most basic interaction genes (Dilute, cream), as well as Aph/Aph^I, and Mahogany (where applicable). We will not discuss any genes that were not part of last month’s article, beyond the e-alleles, in this article.

Duckwing (e+)

I have discussed the e-allele e+ at some length in two previous articles for Exhibition Poultry.  One was titled ‘Pigmentation of the Red Junglefowl’, and ran in the April 2011 edition while the second was titled ‘The Genetic Factors of Silver Phenotypes’ and ran in the December 2011 edition. For a detailed discussion of the interactions of the e-allele e+, the two s-allele mutations, and the Aph and Aph^I factors and modifiers, please refer back to those articles. For this article, I will stay with a simpler explanation, but strongly recommend you review these two previous articles in conjunction with this series.

The duckwing allele is characterized by the so-called “bb red” or black breasted red male, considered “duckwing” due to the triangular pheomelanic area of the folded lower wing. Regardless of the s-allele combination, the male retains the basic “black breasted whatever” format. The female is a combination of melanin, sex-linked and autosomal pheomelanin. Her brown back, orange hackles with a black center stripe and salmon breast characterize the female of this e-allele. The salmon breast, which is her most distinctive characteristic, is the main diagnostic trait of the duckwing female.

The male of the duckwing allele differs little from the males of the e-alleles eb and eWh. The only major variation between the e+ male and the males of ER and E is the presence of the pheomelanic wing triangle, which is absent on the solid black lower wing of the alleles E and ER. It is the female where there is a great difference from the other alleles of the e-locus.

Autosomal pheomelanin has the greatest expression in the male of the e+ allele on the shoulder and back, the outer edges of the main wing feathers, the top of the head around the face and around the outer ring of the hackles and along the back edge of the saddles. The remaining pheomelanic areas are predominantly sex-linked pheomelanin. In the female, the breast is predominantly autosomal pheomelanin, while the back, wing, cushion and secondary tail feathers are a blending of sex-linked pheomelanin, autosomal pheomelanin and eumelanin. The hackle of the female is predominantly sex-linked pheomelanin with the upper head, area around the face and the outer edge of the hackle strongly influenced by Aph, just as in the male.

When silver (S) is the gene at the s-allele, the sex-linked pheomelanic areas are lightened to a cream-yellow tone, but the autosomal pheomelanin is unaffected. Thus silver hens show the strongly salmon breast, and if mahogany is present, the breast, back and shoulders may be deep reddish brown, just as the shoulder of the silver male can be dark reddish brown with mahogany present in conjunction with silver and Aph. Aph^I is required to block the expression of autosomal pheomelanin (and thus also Mahogany) and begin to work toward a fully clean white silver phenotype.

When hens are heterozygous for Aph^I, the breast can be patchy, showing salmon areas and cream areas, sometimes as slight lacing of cream on the salmon breast feathers, and sometimes as patches of cream or even a central area of cream in the center of the salmon breast. Fully homozygous hens for Aph^I show very little color in the breast, with the breast tending toward cream/beige with very little salmon tone at all. While these hens will have a lighter tone of cream with S (Silver), even the s+ (red) hens show a very pale breast of a beige tone when Aph^I is homozygous.

Brown (eb)

On the brown allele, eb, the males are nearly identical to the males of e+, except that they will tend to have more distinctly striped hackles and saddles, and Aph has a somewhat stronger effect on the upper hackle and along the outer edge of the main wing feathers and outer edge of the saddle, than is seen in the e+ male. This is a very subtle point, as males of both alleles show Aph saturation in these areas. In the eb male, it is only slightly stronger in saturation. Otherwise, the males are identical.

The females, however, are another story. In the most basic sense, the major difference between the e+ female and the eb female is the later lacks the salmon breast of the former. The breast of the eb hen is replaced with a combination of the three pigments, just as in the back of the e+ hen. So we can state that he entire body of the eb hen is very similar to the back of the e+ hen. The eb hen’s entire body plumage behaves as the back of the e+ hen also. As the eb hen’s back is a blending of sex-linked pheomelanin, autosomal pheomelanin and eumelanin, we can produce the same range of shades as seen in the e+ hen’s back. For instance, if we have s+ (gold or red) and Aph with mahogany, we see a very dark red-brown body as seen in the Partridge and dark brown varieties. 

If we change s+ to S (silver) and have Aph^I, we get a very clean silver-gray background as we see in the cleanest silver penciled varieties. When we have silver without Aph^I and rather have Aph present, we see a silver hen that is not the clean, crisp black and white of the best silver penciled, but rather the entire body shows a slightly cream tinted under color, sort of like a tobacco stain on white, which is commonly seen in many less clean silver penciled lines. The genetically identical male of this type will also show a yellowish tone to his pheomelanic areas and we call such lines “brassy” in exhibition terms. To get the very clean, crisp “black and white” silver penciled expression, the inhibitor of autosomal pheomelanin is necessary along with silver.

With the eb allele, there is a reduction of the expression of autosomal pheomelanin in the female, while there is an increase in the expression of eumelanin and sex-linked pheomelanin, as compared to the duckwing allele, e+.

Wheaten (eWh)

I would consider the allele eWh, wheaten, to be the opposite of eb, in that it is a reduction of eumelanin and sex-linked pheomelanin as compared to the allele e+, duckwing.

There is little difference visually between the males of e+, eb and eWh. The wheaten males tend to show less (and often none) of the melanization striping in the hackle and saddle, while Aph has a greater saturation in all of the pheomelanic areas. This is especially noticeable when S (silver) is present at the s-allele (even more so when Mahogany is also present), as Aph clearly suffuses all pheomelanic areas more fully and with stronger saturation as compared to either e+ or eb. This some silver wheaten males can show a considerable amount of salmon to dark red coloring in the cream to silver hackle, which can be very confusing if you are not clear to the effects of Aph on eWh.

The eWh hens are the opposite of the eb hens, in that they show a reduction of eumelanin and sex-linked pheomelanin and an increase in autosomal pheomelanin. In short, the entire body of the eWh hen is similar to the breast of the e+ hen, while the blending of eumelanin, sex-linked and autosomal pheomelanin, as seen on the back of the e+ hen and the entire body of the eb hen, is not present on the eWh hen.

At the darkest end of the spectrum, when we see s+ with Aph, Mahogany and melanization on the eWh female, the entire body tends to be a dark brown/salmon tone often called cinnamon, as in the Cubalaya. Without the melanization saturation, we see the normal wheaten female where the entire body is salmon colored, as seen in Malay or some Old English Games. When the wheaten hen is heterozygous for Aph^I, we see a split between the back/upper body and the breast/lower body, where the back is salmon, but the breast is cream colored. With the Aph^I homozygote, the entire body of the wheaten hen is cream colored, as we see in Some Old English Game Bantams that show this very pale form of wheaten.

The addition of silver does not change the expression of Aph/Aph^I in the body of the wheaten hen (as described in the paragraph above). The only major change from silver to the wheaten hen is in the hackle, where the silver gene lightens the hackles from cream to white, depending on the other genes present. However, as I described above for the male of the wheaten allele, the females also show a stronger saturation of Aph in the hackles, especially when Mahogany is present. Thus, one can have a silver wheaten female and still see a good deal of dark red in the otherwise cream colored hackle (some Salmon Faverolle hens show this effect, for example), if Aph is present. The cleanest, palest and most colorless wheaten hens are found when wheaten is combined with silver and is homozygous for Aph^I. Such hens are a solid, pale cream to white color with a bit of black in tail, wing and hackle and can easily be confused with the silver Columbian variety (of which the standard form is on the e-allele eb).

Birchen (ER)

The male of the Birchen allele is very similar to the males of the preceding e-alleles, except that he does not show the pheomelanic wing triangle, has very strong hackle and saddle center stripes and does show a pheomelanic lace at the edge of his breast feathers. This breast lacing is the major diagnostic factor (along with chick down) to distinguish ER from E. The male of the ER allele shows the same effects from Aph and Aph^I as the e+ male and in the same regions. The breast lace is generally dictated by sex-linked pheomelanin though, and this differs from e+. As well, the black wing will show no effect from Aph or Aph^I, due to the full melanization caused by this e-allele.

The female of the ER allele is nearly identical to the male, except that she does not have a pheomelanic shoulder or saddle. She is basically fully eumelanic (black) with a pheomelanic hackle with black stripe and pheomelanic lacing on the black breast. On this allele, the strongest effect of Aph is on the head, upper hackle and edge of hackle, as seen in the hens of other alleles. The breast lace of the female is also determined by sex-linked pheomelanin.

Only when other genes, such as Dark Brown (Db – aka ‘ginger’) or Db with Columbian are added to this allele, does the effects of Aph or Aph^I become noticeable. While Aph and Aph^I have little visible effect on the unmodified form of the ER allele, either (or both) of these factors can be present and can show their effects when ER birds are crossed out to birds of any of the previous e-alleles or when other modifier genes are present.

Extended Black (E)

Extended Black here does not refer to a solid black chicken. In fact, the phenotype on un-melanized E is nearly identical to ER, except that there will be no breast lace in either sex and the hackles/saddles will show even heavier melanic striping than in ER.  The effects of Aph and Aph^I is the same on E as on ER: minimal. The male will show the effects of Aph in the same areas as all the proceeding males, while the females will only show the effects on her head, upper hackle and the outer ring of the hackles, as in the proceeding females. One major difference between E and ER is that while ER can show the effects of Aph and Aph^I when modifier genes such as Db and Co are present, E is not effected by Co or Db and thus does not show the effects of Aph or Aph^I when either of those modifications are present. However, all E birds carry Aph and/or Aph^I, and so it is a consideration when outcrossing the other alleles to this allele, if in no other case.