Download GENETIC CONTROL OF MELANIN PIGMENTATION IN THE FOWL

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GENETIC
CONTROL
OF MELANIN
PIGMENTATION
J. Robert Smyth, Jr.
Department of Veterinary and Animal
University of Massachusetts
Amherst, Massachusetts
IN THE FOWL
Sciences
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Genetic
Control
of Melanin
Pigmentation
in the Fowl
Variations in melanin pigmentation of the skin and its epidermal integuments
have long attracted the interest of poultry fanciers and breeders, and were
among the first phenotypes to be subjected to genetic analysis following the downing of Mendelism at the beginning of this century.
Since then we have learned
much about the inheritance of melanization,
particularly of the feathers, although
the genetlc bases for a number of phenotypes have not been determined as yet. The
purpose of this presentation
is to review and update information on the inheritance
of melanin pigmentation
in the fowl.
Included will be consideration
of some
practical aspects of the subject, such as the use of plumage color genes for sex
identification.
In addition, I hope to impress you with the potential of melanin
pigmentation as a genetic model for other physiological
systems.
After reviewing our present knowledge on the inheritance of melanization one
must be Impressed with its genetic complexities,
particularly the importance of
genetic interactions.
These are readily demonstrated between the individual
plumage color genes, and also between these and certain gene complexes that have
not been separated or worked out as yet.
After summarizing some of our own recent
work at the University of Massachusetts,
it was surprising to observe the number
of different genetic routes to identical, or nearly identical, phenotypes.
Furthermore, many relationships between alleles and non-alleles appear to be only
as consistent as the specific genetic background on which they are observed.
We
have here then a physiological
system that is relatively unaffected by environmental components and controlled by a number of identifiable, qualitatively
inherited genes plus polygenic modifying complexes.
Various interactions between
these culminate in the final phenotype.
Therefore, one could consider plumage
color a polygenic trait and a simplified genetic model for other quantitatively
inherited traits.
Although beyond the scope of this discussion,
the melanin system offers a
promising model for mechanisms underlying cellular differentiation
and gene
regulation in eukaryotes.
In this respect, I would like to acknowledge the very
interesting and exciting work on the genetic control of melanization by Dr. John
Brumbaugh and his associates and students at the University of Nebraska.
Melanin
Pigmentation
Melanin pigment is found in many parts of the body.
Cutaneous locations
include the feather, other epidermal structures such as the scales of the shank
and the beak, as well as the dermis.
It is also found in such ocular sites as
the iris, ciliary bodies, choroid and the pigment epithelium of the retina.
Other locations can include the testes, abdominal fascia, intestinal mesenteries,
and throughout the body around nerves, blood vessels and ducts.
A significant body of literature has been compiled on the developmental
aspects of the melanin producing cell, the melanocyte
(for review, see Lucas and
Stettenheim, 1972; and .Searle, 1968).
With the exception of the retina, all
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i
melanin found in the body comes from cells which have their orlgln in llthe
embryonic neural crest.
The undifferentiated
melanoblasts mlgrate from the
neural crest and populate certain body tissueswhere
they differentiate
into
pigment producing melanocytes.
Melanin is found in the forms of pigmelnt
granules, these cytoplasmic organelles,
being called melanosomes.
The_ fu]-ly
melanized melanosome
Is formed following the attachment of the pigment! fraction
to the proteln matrix of the premelanosome.
The work of Maul and Brumbaugh
(1971) and Brumbaugh et al. (1973) suggests that the Golgl-associated
:Ityrosinetyroslnase pigment complex and the structural protein of the premelanosome
involve.different
developmentalprocesses,
each independently susceptible to
mutational alterations.
Melanocytes of the fowl can produce either eumelanin (black) or pheomelanin
(buff, red or brown), although the latter is found only in the feathers.
These
pigments differ biochemically, although they share the same synthetic pathway
through the formation of dopa quinone.
In addition, each type of pigment is
attached to a specific protein matrix that determines the different me:lanosome
sizes and shapes (Brumbaugh, 1968).
Each basic pigment can be modifie_ by
genetic factors, e.g_., black to blue eumelanin by alteration of the structure of
the premelanosome.
The many phenotypic variations in pheomelanin are also
the
i
result of mutational changes in melanosome concentration and dlstributilon.
The
genetic bases for these may be polygenic or the result of individual genes such
as silver (S) or cream (ig).
,
Whether a melanocyte will produce eumelanin or pheomelanln depends on its
own genotype, as well as its cytoenvironmento
Brumbaugh (1967) has shown by
embryonic grafting experiments that the alleles at the E_-Iocus of the fowl are
autonomous, yet with the exception of the most dominant E--allele the decision to
make black or red melanin depends on the local tissue environment.
Some obvious
environmental differences affecting melanocytes at the individual blrdiilevel are
sex and feather tract specificities.
Brumbaugh has suggested that the_interaction
between the genotype and its environment takes place in the zone of differentiation of the developing feather.
He believes that the key en_Ironmental
effect is related to feather growth rate with rapid movement of melanoSlasts
through this zone favoring eumelanin synthesis.
Eumelanin
Distribution
The major factor determining a colored plumage pattern is the distributlon of
eumelanin.
Once black pigment is produced in response to the pigment _ell
genotype x local cytoenvironment
stimuli then pheome!anin formation is probably
precluded in that melanocyte.
In line"_ith this, Brumbaugh (1971) has suggested
a model whereby eumelanogenesis
occurs at an earlier stage of development than
does pheomelanogenesis.
Therefore, the first genetic determination wil!l decide
the location of eumelanin with pheomelani_ then being potentially present elsewhere.
;
Two useful descriptive terms for eumelanic distribution are "primary pattern"
and "secondary pattern."
The primary pattern involves the distribution of
eumelanin on a zonal or regional basis, often involving one or several iifeather
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tracts (as in the wild type male or the Columbian pattern).
The secondary
pattern refers to the distribution of eumelanin within the individual feather,
e._., stippling, pencilling, barring, etc.
These terms were proposed by Kimball
(1953) and applied to classify plumage color genes into primary and secondary
pattern genes.
Since, as pointed out by Morejohn (1955), come genes may affect
both primary and secondary pattern, their classification on this basis is Incorrect.
However, it is still useful terminology to use in a general way to describe genes whose major effect may be on either primary or secondary patterns,
_._., E versus B.
In any event, the terms are of valueiin describing the eumelanin
distribution within the plumage.
As I visualize the situation, the genetic determination of primary plumage
pattern revolves around the genotype at the E--locus and its modification
by other
genes with primary pattern effects.
This idea is presented diagramatlcally
in
Figure I. Each of the E--alleles determines a specific primary pattern, varying
from the extreme black distribution of the E--allele to the greatly reduced amount
present in the wheaten (eWh and _Y) females,
With the appropriate modifying genes
the eumelanin distribution associated with any of the E--alleles may be moved to
the extremes, solid black or essentially non-black Columbian-like
(as in the
clear Buffs).
The black-intensifying
factors shown in Figure I include melanotlc, M__L,which
is even more effective when linked with lacing, Lg (Moore and Smyth, 1971).
As
will be pointed out later, we have evidence for other major eumelanln intensifiers, but these have not been isolated and studied as individual mutations.
In
the presence of the maximum intensifying effect, even the reddish wheaten female
pattern becomes solid black.
As might be expected, there are many phenotypes
that are intermediate between the non-intensified
distribution associated wlth the
E-allele and solid black coloration.
Several
geneshave
been
isolated
that further
restrict
the black
distribution
associated with the unmodified E--alleles, primarily in the direction of a
Columbian-like
pattern.
These include Columbian (C_oo),mahogany (M_h_h)
, dark brown
(Dl0) and dilute (Di).
In addition there appears to be unidentified modifying
genes such as those proposed by Somes and Smyth (1966) which tend to behave as a
polygenic complex.
Various genotypic combinations of the above can account for
the many modified phenotypes ranging from a wild type male with slight red tipping on its black breast to a phenotypically non-black Buff Orpingtono
The E-Locus
At the present time eight alleles have been proposed for the E-locus, including extended black (E), birchen (ER), dominant wheaten (eWh ),_ild
type
(e_+), brown (e__
b ), speckTed head (_s _and
recessive wheaten-(eY
). The above
are listed in order of decreasing dominance°
Morejohn (1955) _irst described the
E, e
+
, e__
b , e__
s and eY alleles.
These were verified by Brumbaugh and Hollander
(1965), who also added-the e__
Wh and e bc alleles.
In our work we have verified the
allelic relationship of E, e+ and e_ (Smyth, 1965), as well as e_Wh , e_bc and
eY (unpublished data) and suggested the addition of the ER allele (moore and Smyth,
_972a).
The latter had been proposed as an E-allele earl--ierby Kimball (1954).
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_SOLID
BLACK
l'
OTHERS
I.
MI
?
[Lg ]
:q
I
Co
Mh
I °°
Di .
COLUMBIAN
Figure
1
OTHERS'?
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Of the above, we have not knowingly worked with eS allele, and have some current
reservations about the identification of a specific ER allele.
Because of the importance of the _-alleles an attempt to compare their effects
on the primary plumage pattern is shown in Figures 2a and 2b.
Descriptions
supplemental to the illustrations follow:
Adult males.
There are only three basic adult male phenotYpes with two of these,
E and ER showing considerable variation°
E results in the greatest extension of black pigment, while the wild type male is non-solld black on the
head, hackle, saddle, wing bow and wing bay° With the exception of _ and
_R, all of the other E-alleles result in a wild type adult male pattern.
The _R allele has been proposed to have an intermediate phenotype, resembling
+
e
, but having black flight feathers (wing bays).
Adult
females.
These females have essentially
E
-secondary
pattern°
_R
- Birchen females have non-black
black
plumage
breaks on their
with
no
heads and hackle.
Their bodies may be solid black or modified by fine stippling.
Non-black marginal lacing on the upper breast of males and females
of some birchen breeds appears to be due to modifying factors
(Cote, 1976)o
- Dominant wheaten females have little eumelanin, that present being
limited to the wings and tail.
The overall body color is of a
salmon-brown color, similar to that seen on the salmon breast of
the me+ female°
The breast coloration is lighter, becoming more so
ventrally°
eWh
e+
eb
es
-ebc
m
eY
solid
=
- The wild type female has a brown body with darker stippling (a
secondary pattern) dorsally°
The breast is salmon-brown
In color
and shows no secondary pattern°
- The brown female closely resembles the wild type, but noes not
have the salmon breast°
The breast shows the same secondary
pattern that is present in the rest of the plumage.
Although
eb/e b females can be well stippled (dark brown Leghorns), there is
a strong tendency to show pencilling.
This probably explains why
at least some pencilled breeds carry eb (Smyth, 1965; and Brumbaugh
and Hollander, 1965) 0
- According to Morejohn (1955), eS/e s females are "similar to e b
homozygotes but not as dark, ioeo, feathers were not as darkTy
stippled°"
- The buttercup allele also results in a female that closely resembles
the brown phenotypeo
Although e bc is the E--allele of the buttercup
breed, the phenotype of the latter is the result of an interaction
between ebc and the Db mutation (unpublished observations).
- Recessive wheaten females are phenotypically
similar to dominant
wheatens.
Chick downs_
Extended black down is black on the dorsal and lateral surfaces,
while the ventral surfaces and the wing tips are cream-colored or
white.
Homozygotes often have a small white dot on each side of
the lower forefaceo
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E
ER
_.
eWh
e.l.
Figure
',
i!
2a
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eb
!
.- eS
ebc
eY
"_
• Figure
2b
-
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ER
I
-
eWh
Birchen
down resembles
that
of E, although
the non-black.area
on
the ventral
surfaces
may be reduced
in some cases.
- The down of dominant
wheaten
is essentlally
clear
cream i!n
color
'1
although
small
dorsal
head spots are common°
An occasional
chick,
usually
a female,
may show a faint,
broken
trace
of the dark lateral
black
stripes.
- The wild type down pattern consists of a dark brown median dorsal
stripe that continues onto the dorsal surface of the headl. On
either side of the back are narrower, dark brown, lateraIIstripes
separated from the median stripe by two yellowish-whlte
stripes.
The ground color is of a lighter tan shade, being Iightest on the
ventral surfaces.
+
e
e__
b
- The brown chick has the darker brown pigment more evenly distributed
over the dorsal surfaces and the head.
Some reduced evidence of the
yellowish-white
stripe is _fte_ evident.
There is no sharp break Tn
the head Color as in the e /e chick, although some lighter shading
of brown may be evident in front of the eyes and/or alongJthe front
line of the comM.
es
•.7
- According to Morejohn (1955), the pattern of the body resembles the
wild type, but in the head region the dorsal head stripe is broken
and irregular.
Brumbaugh and Hollander (1965) refer to this pattern
as "blurred°"
i
e bc
- Our_ebs/ebCchicks_ show a back stripe similar to wild type, but the
yellowish-white
stripe is distinctly wider.
The dorsal head stripe
is also broken and irregular, presumably resembling eS/e§,
eY
- The recessive wheaten down resembles that of the dominant allele
-(e_wh), however, head spots and faint back st_iping are more common
in the eY/e Y chick°
Dominance relationships between the E-alleles show some variation but in
general
follow
the order
listed.
Dominance
of the down and adult
female patterns
appro_Ehe_ completeness,
except for certain combinations
involvlng domlnant wheaten.
Tile e"U/e-and e""/e _ downs are both reduced wild stripes, somewhat
resembllng
the
0
0
01
buttercup down_
T_ese genotypes result in adult females with Intermedlate patterns,
reducing the amount of secondary pattern and increasing the salmon-brown coloration
on the body.
The e Y allele appears to be completely recessive in all cases.
Eumelanin
Intensifiers
A number of investigators have found that it is possible to produce black or
nearly black fowl by accumulating eumelanin intensifiers on a non-E back:ground (for
review, see Moore and Smyth, 1971).
We have developed such a line and call it our
"Recessive Black line" (RBL).
It carries no E, being homozygous for the e_b allele.
Both sexes have completely black plumage as _ults,
although the males in thls llne
have white undercolor.
The latter is not necessarily a part of the "recessive black
complex" as such males with dark undercolor can be observed among cross progeny.
The
shanks and beaks of these adults are non-black.
Although our line is ebTe b, it is
possible to produce the phenotype on e + or e Wh , although it takes more modifiers
to eliminate the salmon coloration in the female breast plumage.
Down color In our
RBL is much darker than the typical e b brown down indicating that in selecting for
completely black adults we have included some genes that also increase down
eumelanization.
However, it is not necessary to have the darker downs to produce
solid black adults.
In several of our gene pool populations, such adult_ develop
from typically brown or wild type downs.
I;
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Our present data indicate that the RBL line carries a number of eumelanin
intensifiers, but at this time only two individual genes have been isolated for study.
These include melanotlc (MI), one of the line's major eumelanlzets, and lacing (L__gg)."
These two mutations are linked with approximately
10% crossing over between the two
Iocl (Moore and Smyth, 1972).
Melanotic results in a general, but variable, darkening
of the adult plumage accompanied
by a major effect on the head and hackle.
It has no
known effect on down color.
As expected, lacing has its greatest eumelanizing effect
on the feather margins, and this effect is intensified in the presence of MI.
Columbian-like
Eumelanin
Inhibitors
A number of genes appear to act as eumelanin inhibitors and modify the plumage
toward the Columbian pattern.
These are particularly effective against the black
breast of wild type-patterned males, and reduce general body eumelanin In non-E
females.
Three such mutations that have been well established
Include Columbian
(C__oo),
dark brown (Db) and mahogany (M_hh). It would appear that there are other as
yet unidentified genes in this category, possibly even a few with major effects.
The Co mutation was originally found as a hypostatic gene in a recessive white
line, and-later studied in Buff Brahmas by Smyth and Somes (1965).
It is probably
the same as the ginger gene isolated from a Buff Minorca by Brumbaugh and Hollander
(1966).
An attempt to show some of the phenotypes resulting from various Co genotypes is shown in Figure 3. Homozygou_ C2 with eb/ebresults
in a standard Columbian
pattern In the adult plumage.
Adult e-/e- Co/Co males are similar, but females of
this genotype tend to have a reduced amount of secondary pattern left on their backs.
Heterozygous Co is relatively effective in the male of either genotype, but females
show intermediate back eumelanization.
In addition to its effects on eumelanin,
Co also changes the color of pheomelanin to an orange-gold.
A single dose of Co
w-Tll change the salmon-brown color of the female e + breast and e__
Wh body feathers to
orange-gold.
The expression of Co in the down is extremely variable and depends on the
accompanying genotype (Figure 3).
In general, it is the result of interactions between Co._ the E-locus and a polygenic eumelanin intensifying complex.
In the
absence---of the Tatter and in the presence of e b the down color on the dorsal surfaces
is light gray or cinnamon (s+) depending on wh--ethersilver (S) or gold (s
+)
is
present.
The phenotype is similar on an e_
+ background except that the dorsal back
stripe is more prevalent and in some cases the outline of the head stripe is also
apparent.
In the presence of eWh/e Wh the back surfaces are essentially clear white
or gold.
The addition of the polygenic intensifiers increases the amount of
eumelanin until the dorsal surfaces are completely black.
At the maximum level of
expression even the belly is gray, and the only non-black area is in the extreme
foreface area.
The most heavily eumelanized chicks are usually females, and these
can easily be confused with E/- chicks.
At the appropriate
level of eumelanization,
and in the presence of a spec_ific modifying factor, eb/ebCo/Co chicks can be auto_
sexed with a high degree of accuracy (Somes, 1971; and Malone and Smyth, 1975a).
The autosexing factor apparently interacts with the sex hormones to result in a
white dorsal surface on the wing and reduced ventral eumelanization
in male chicks.
The Db mutation
was originally
isolated
from the Fayoumi
by Moore
and Smyth
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e+le + Co/Co
ii
;bleb
e(Cinnamon
)
ebleb Co/Co
[Black
Back]
i,
eb/e b Db/Db
Figure
3
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(1972b).
These workers proposed the Db worked in concert with Co to restrict
eumelanin in the ER/E R Barred Fayoumio
When Db was extracted and recomblned with
e + and_e b , it was found to result in modified---Columblan-like patterns.
Homozygous D__bb
males have the black-tailed silver or gold phenotype, while the females.
are also modified Columbians but show someresidual secondary pattern (usually
autosomal barring) on the ventral surfaces of the breast and posterior back plumage
(Figure 3).
Heterozy_ous females are similar but with more secondary pattern and
in the presence of e T, the salmon breast is evident, but diluted.
The hetrozygous
male has non-black tips on otherwise black breast feathers.
In the presence of some
as yet unidentified modifier, D_Dby'db
+ .,4 + or eb
males may have a brown breast°
The D_b_b
gene in combination with eb-C/eoc and autosomal barring represents the key
genetic makeup of the Buttercup breed.
In addition to its effects on eumelanin Db
also alters the color of pheomelanin.
The resulting pigmentation has a distinctive
orange-tan or burnt-orange color
All of the downs associated with the E-alleles are modified by Db, particularly
when it is homozygous.
The effect on E_ and-E
R_ is to modify the black down to a dark
brown.
This may vary from a dark brown foreface to a completely brown chick dependl'ng
on Db dosage and the residual genotypeo
When heterozygous,
it widens the yellowishwhite stripe one + , e__
b and ebc chicks and reduces the dark brown head markings.
When homozygous,
It removes most of the dark dorsal striping and lightens the ground
color to a cream (Figure 3). With the buttercup allele, D_bbleaves only a few head
spots and a faint remnant of the lateral back stripe
The mahogany (Mh___)
gene was isolated from a Buff Minorca by Brumbaugh and Hollander
(1966), and we obtained this mutation from Dro Brumbaugh several years ago.
MahoganT's
effect on primary pattern in the female is to restrict generally the amount of eume]anin
in the plumage, particularly on the breast back and the wing bows and fronts.
In the
presence of sex-linked gold (s+), the phaeomelanin
is dark red or mahogany In color.
In the +e
female the salmon breest also becomes dark red in color.
The major effect
of__Mh on the adult male is to restrict black from the base of the pennaceous part of
the breast feathers.
The amount of black left distally is less in homozygotes than
In heterozygotes, some of the breasts of homozygotes resembling the secondary pattern,
spangling.
In addition, there is a general degree of reduction in eumelanin in the
back and wing areas of the plumage.
Our observations confirm those of Brumbaugh and
Hollander (1966) that Mh does not affect down color°
Inheritance
of Some Columbian
Phenotypes
It is now apparent that there is no single genotype for the range of phenotypes representing variations in the "Columbian restriction" of eumelanlno
Once
generally attributed to e, a suggested allele of E (for review, see Hutt, 1949), we
now know that these patterns result from interactions between genes at a number of
different Iocio
In order to distinguish between the various Columbian-like
phenotypes, Smyth (1970) classified:them
into three groups, including the Columbian,
black-tailed
red (or silver) and the Buff (or clear silver).
The standard Columbian
pattern is described by the American Standard of Perfection
(1962) and Is found in
such breeds as the Buff Brahma and Columbian Plymouth Rock.
It is characterized
by
black central stripes along the rachis of the hackle and saddle feathers° The
black-tailed red phenotype is found in the New Hampshire where the black is restricted to the wings and tail.
In these birds the hackle feathers do not have
black center stripes, and any eumelanin in the saddle is reduced well below the level
i ..
_
,
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In the standard Columbian.
The buff phenotype is characterized
by the phenotypic
absence of eumelanln, although it is hard to find specimens that do not lshow
small amounts of black in the tail.
d
• "
The Columbian-patterned
Buff and Light Brahmas were found to be eb_e b at the
E-locus and homozygous for the Co gene (Smyth and Somes, 1965)o
The latter is
•
presumably also responsible for-_-he orange-g01d color of the pheomelanln in the Buff
Brahma.
In contrast, Smyth (1970) reported that New Hampshires carrled.eWh atlthe
E-locus, as well as Co.
More recently, we have also isolated mahogany (M-h) from
our New HampshJreso
In these studies, results of crosses between New Hampshires
and Light Brown Leghorns suggest that some of the former carry a light down factor,
which when the New Hampshire is used as the female parent results in lighter
colored down in the male chickso
This factor appeared to affect only the down
color, adult plumage being unaffected.
It is possWble that this may be the same
dominant sex-linked gene reported by Hertwig and Ritterhaus and referred to as light
down, Li (as reported by Hutt. 1949)_
i
Brumbaugh and Hollander (1966) hypothesized that the Buff phenotype of the Buff
minorca is due to the combined effects of mahogany (Mh_), ginger (G_r- probably our
Co), dilute (Di) and champagne blond (cb) in combination with recessiveLwheaten
h_h_tY
).
Inter-_tin_ly, the Buff Minorca that these workers analyzed proved to be
erozygous e°C/e_7 at the E--locus. They also suggested that Rhode Island Red and
Speckled Sussex were eY/eY , while Malone (1975) analyzed the genetYc makeup of an
exhibition Rhode Island Red and found it to be heterozygous.fom=.domlnant
and recessive wheaten (eWh/e y ). Malone also recovered Mh from this bird and suggested
that it was also hete_ozygous
for Co. These observations again show how different
genotypes can result in similar plumage patterns°
Analyses
Based on the observations
of Solid
of Moore
Black
Plumage
and Smyth
(1972a), as well
as otiher un-
published observations made at our station, it appeared desirable to anallyze the
genetic makeup of a number of genetically diverse individuals with solid black
plumage.
Since we were interested in the importance of eumelanJn intensiflers on
E-related blacks, the study was limited to birds that had typical extend led black
,d--ownoThis analysis was ably conducted as an MoSo thesis study be one of my
students, Ronald Cote.
He analyzed nine different males, all showing complete
extension of eumelanin throughout the plumage.
Of these, two carried sex-linked
barring (B_J, two were autosomal blues (BL/bl), and one was a black synth_etJc
homozygous for henny feathering (Hf).
Six of the nine were from pureIines, while
three were from segregating gene pool populations°
All birds were analyzed by
studying F1and backcross progeny from crosses to our Light Brown Leghorn l (e+)
tester line.
Some additional F2 and testcrosses were made where deslrablle--and/or
feasible.
Unfortunately,
it was notpossible
tO include detailed comparisons of
,homozygous and heterozygous
The results
the complexities
single phenotype
FI or backcross
Eo
--
ii
of this study proved to be very interesting, and again demonstrated
of the many different genetic interactions that can result Tn a
(Cote9 1976).
With
males heterozygous
the exception
for E had solid
of the benny
black
featheredil cross,
plumage.
Phenotyplcally
no
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these varied from dark birchen to standard birchen in pattern°
Of the nine
original black males only six were found to be homozygous for E° Backcross
segregation data indicated that all of these carried black intensifiers including
melanotic (MI.), but some were non-laced in the repulsion conflguration_ Ml-lg
+.+
A pure Exhi-bTtion Barred Plymouth Rock bantam was found to be MI-Lg/ml -Ig , and
surprlsingly, appeared to be heterozygous for Coo
Two of the three phenotypically
"extended," heterozygotes were from gene pool ITnes and were E/e b, while the other
was E/e+, The latter was a pure Exhibition Black Old English bantam and carried
neither__MI
nor
these
effectively
Lgo
This
bird
was found to carry
added sufficient
eumelanizing
other
activity
eumelanin
_ntensifiers
and
to change the hetrozygous
E__phenotype
to a solid
black
plumage°
The two E/e b heterozygotes
were also found
to be heterozygous
for Co, which was effectively
masked in both°
Interesting,
these
two males were from different
and unrelated
synthetic
gene pool
lines°
Unidentified
modifiers
other
than Co were found to reduce
the extension
of black
pigment
in the breast
plumageo
of heterozygous
E, while
others
progeny°
Whatever
their
identity
intensifying
complex°
Expression
of
Some of these were effective
only
in the presence
also modified
breast
coloration
in the wild
type
they all
could
be masked by the E-eumelanin
Silver
and Gold
As mentioned
previously,
pheomelanin
of feathers°
in the presence
of sex-linked
a number of shades of red, brown or buff,
in Adult
Plumage
is
found only
in the non-black.portions
s+ , these areas may be of. any one of
depending
on modifying
genes,
or
pheomelanin
may be removed by the silver
(S) allele°
variation
in the ability
of _ to remove pheomelanin,
on several
additional
genetic
interact_onso
There
is considerable
_ts effectiveness
depending
One of the basic
interactions
affecting
expressivify
of the S--alleles
Involves
the E-locuso
Although
S is readily
expressed
in the non-black
plumage of the male
wild-type
pattern
associ'-ated
with
eWh, e+, e b, e bc and eY , this
is not the case for
some of the female
phenotypeso
Fo7 example_
the salmon-brown
breast
of the e+female
is not eliminated
by hemizygous
S, although
pheomelanin
in the rest
of the plumage
is removed
(eogo,
Silver
Duckwing
pattern)°
Similarly,
the salmon-brown
feather
pigment
of dominant
and recessive
wheatens
is also
resistant
to sllver,
suggesting
that
the salmon-brown
pigment
observed
in these
particular
phenotypes
is the same,
or at least
very
similar°
In contrast,
S is effective
in females
with E.__
R , __
e b or
ebCphenotypeso
As demonstrated
by Malone
(1975),
the addit!on
of Co changes
the +e
and wheaten
salmon-brown
plumage giving
it an orange-gold
coloratlono
Silver
was
found to be completely
effective
against
the orange-brown
pigment
associated
with
+
+
+
+
Co.
Therefore,
an e /e
S/-co
/co female
has the silver
duckwing
pattern
with
a
salmon breast,
but the addition
of a single
Co allele,
changes
the breast
pigment
so that S can express itself°
The result is a white breast on a bird with some
dark stippling left on the back and sides of the wing°
Similarly Co changes the
wheaten pigment, so that it is also removed in the presence of So
As previously demonstrated, dominant white (_) is relatively ineffective
against pheomelanin
in post-down plumage.
We have observed that both the salmonbrown and orange-gold feather colors maintain their identity and are readily discernible in I/i+ individuals.
-79-
The Expression
chick
Sex-linked
silver
down.
This
is
of
Silver
and Gold
in
the
Down
also shows marked variability
_n its
of considerable
practical
significance
expression
because of
i!n the
the interest
in using
the S, s + alleles
in sex-linked
crosses
in order
to identify
sex by down
color.
Domlnant-white
(I)
is also usually
included,
since
I/i + does not! suppress
the expression of gold (s+) in the female chicks°
Male chicks (I/i+ S/s+ from
such crosses are essentially white due to the presence of the S-alleleo ! For this
cross to result in a h_gh degree of sexing accuracy, it is necessary that the
pheomelanin
intensity in the s_+/- females !s readily distinguishable
from Its
absence in the S/s+ males,
i;
George Malone, another recent graduate
the expression of S and _+ in the down when
student of mine, conducted a' study on
in combination with specific: color
genotypes In the presence and absence of _/_+ (Malone, 1975; and Malone and Smyth,
1975b) o As previously described, the _-locus determines the presence and absence
of the black and brown pigmented down°
Silver and gold are not expressed In the
presence of these down pigments°
Therefore, they cannot be identified iln the brown
areas of the dorsal back and head stripes in the +e chick; however, silver is
expressed in the non-striped face and in other areas that are tannish colored in
the gold, wild type chick°
When I/i+ is added, silver and gold differences can
be detected by the presence of gold pigment in the face and in the area of the nonbrown lateral back stripes°
However, +e
is not a common allele in commercial
stocks,
and therefore,
this combination
is infrequently
encountered
in the field.
Silver and gold is more difficult to identify on an eb/e b background due to
the fact that the brown pigment is extended over a wider area of the chick°
The
darker the shade of brown in the e_b chick, the more d_fficult it is to sleparate
the silver and gold phenotypes with accuracy°
The addlt_on of dominant :white
further compounds the problem in this case°
The e__
b allele is common Jn irecessive
white stocks, and therefore, is often found in meat stocks (author's unPiubllshed
observatlons)o
The two wheaten alleles (eWhand eY) suppress the expression of pheomelanin
so that it is very difficult to differentiate
between silver and goldo
In the
presence of I separation of S/s+ and s_+ /-chicks is almost impossible.
According
to Morejohn-_1955),
Dark Cornish carry eY/e Y, while we have identified e Wh as
the E-allele in a different strain.
This suggests that White Cornish lines
probably also carry the wheaten alleles, and explains their presence in modern
Cornish-based meat stocks.
Fortunately, as it does in adult plumage, Co has a positive effect on
silver-gold differentiation
(Malone and Smyth, 1975b) 0 The addition of a single
Co allele enhances this difference in the non-brown, lighter "ground" areas of
t--hedown.
In combination with wheaten, gold intensity is increased by --C°to the
point where S-s+ sex-linked crosses provide readily identifiable sex identlfication.
In fact, chicks of the basTc I/i+ eWh/e Wh Co/Co (or Co/co + ) pro¥ided
the most accurate sexing using the S and s+ alleleso
This difference can be
further facilitated by the accumulat-lon _ unidentified modifiers that I:htensify
the red coloration°
Such factors
were
found
by Malone
(1975) to be carriljedby
-80-
the New Hampshire
and Rhode
Island Red Breeds.
The previously mentioned black-back down factors that are associated with
Co can create some confusion when attempting to develop new lines for use In
silver-gold sex-linked crosses (Malone and Smyth, 1975a)o
The eumelanlzed areas
on the dorsal surfaces of the down mask the expression of silver and gold, and
In extreme cases S ands+
can only be identified in the extreme foreface.
When
I is added, accuracy of the silver-gold differentiation
may be reduced to an Impractical level.
The Co-related eumelanin intensifiers have their maximum expression in combination---with meb, but can also confuse sex Ident_flcation on e+o
These intensifiers have been found to be common in recessive white stocks (author's
unpublished observations).
Fortunately, e__Wheliminates most or all of the C_oorelated black-back down effect.
This is further reason to have stocks designed for
silver-gold sex-linked crosses homozygous for wheaten, particularly dominant wheaten°
)_
A number of commercial egg lines have been developed that sex by use of the
S and _s+ alleles with I/i+o Egg line breeders have an advantage in that the Rhode
Island Red and New Hampshire, on which most of their crosses are based, are
homozygous for several key plumage color genes, eogo, Co, s+ , gold intensifiers,
and probably eWhor _Y.
Therefore, the introduction of S and I results in good
sex identification.
Meat breeders have found the development of such a cross more
difficult.
As suggested by Malone (1975), this is probably due _n part to the
fact that modifying genes that help to produce a white feather have accumulated
In
white meat stocks.
These may include a high incidence of E, and a low incidence
of Co, and the wheaten alleles°
In addition, white-plumaged
stocks carry a variety
of hypostatic genes that can prove troublesome on some colored phenotypeso
Secondary
Pattern
Genes
The numerous and variable phenotypes involving eumelanin distribution within
the individual feather provide another interesting genetic model°
Specific genes
associated with secondary plumage pattern interact with the major determinants of
primary pattern, sex, feather tract, and environmental
factors such as growth
rate.
The inheritance of a few of the secondary patterns has been determined, e.g,
sex-linked barring (B_), single black lacing (Lg), and mottling (mo). On the other
hand, the genetic bases for most secondary patterns still need to be clarifled and
related to the total picture°
Since the subject is too extensive to be covered
in any detail herein, I suggest Hurt (1949) as a review source of the earlier
work.
More recently, Kimball (1953a, 1953b, 1959, 1960a, 1960b) has presented
some interesting ideas on the complicated
interrelationships
between stippling,
pencilling and autosomal barring°
A good example of how a secondary pattern phenotype results from the combined effects of several different genes is the inheritance of single black lacing
(Moore and Smyth, 1972c).
The plumage phenotype is exemplified by the Silver and
Gold Laced Wyandotte varieties.
The basic primary pattern was found to be
standard Columbian as determined by homozygosity for Co, and eb at the E-Iocuso
The black lace is added to this phenotype by the combined efforts of the lacing
(Lg) and melanotic (MI) mutations°
As shown in Figure 4, these linked genes
combined efforts are required for the final desired phenotype.
Lacing alone
-80a-
Lg-MI/Ig-ml
Lg-MI/Lg
Lg-MI/Ig
-ml
-MI
Lg-MI/Lg-MI
I
I
Figure
4
-81-
results in a black tip, while eumelanin is extended proximally along the margin
when M__II
is added.
When MI-Lg are found in the absence of Co, then the lacing Is
poorly expressed and associated with secondary pattern effects in the center of the
feather.
Recent observations
by Cote (1976) suggest that the linked combination of
M_l=-Lg is also responsible for the black marginal lace found on blue plumage "
Bl./b_J). It is suggested that the blue genotype is ineffective against
eumelanln present in association with MI--L_. This also leads one to speculate
on the role of these mutations in the black hackle and black plumage of the Blue
Andolusian Male.
Melanization
of Other
Tissues
Studies on the genetic bases for melanization of tissue other than feather
have mostly concentrated on pigmentation of the shank and abdominal facia.
In
either case there are still unanswered questions about the inheritance of these
traits.
Shank melanization
is the better understood of the two. A sex-llnked
gene, +,
id
is associated with the deposition of dermal pigment.
In addition,
it has been demonstrated that some plumage color genes also affect shank color
(for review, see Hurt, 1949).
The IE-allele in particular has been related to
epidermal melanization.
However, Core's (1976) observations on shank pigmentation made in connection with his analysis of black plumage indicate that the
relationship of E to shank melanization
is more complicated than indicated by
previous workers.
A number of studies (Jaap, 1958; Huntsman et al., 1959 and
1960; and Kuit, 1967) have indicated that genes associated with plumage and
shank pigmentation also affect melanization
in the abdominal region.
These
studies revealed a number of interactions between major genes, although some
observations were at the phenotypic (eog., "Columbian") rather than at the
genotypic level.
Leon Wilkins, another recent graduate student at the University of
Massachusetts,
conducted a study on melanization of shank, abdominal fascia
and testes.
This work was the subject of his 1975 Master's thesis_
His main
objectives were to study the effects of major plumage and shank color genes on
melanlzatlon
in these areas, as well as to compare the responses of the three
different tissues.
He found that in general as the amount of feather
eumelanin increased so did pigmentation of the shank and fascia, while the incidence of testes melanlzation decreased.
In most of the 13 different stocks
studied the correlation between shank and abdominal pigmentation was significantly higher than in the other comparisons°
The correlations between abdominal
and testes pigmentation were intermediate, while the shank-testes correlations
were low and significant
in only one line. Wilkins attributes these relationships to differences
in the migratory pathways of the resident melanoblasts,
as
well as the final tissue environments of the pigment cells.
Of the identifiable genes affecting melanization,
Wilkins (1975) found the
major inhibitors to be I and eWh.
His observations on I confirm those of earlier
workers, while the wheaten effect probably was behind some of the previous reports concerning "Columbians."
The most consistent melanin enhancer for all three
tissues was id__
+, the gene associated with dermal melanization
in the shanks.
-82-
HIs data also showed that a gene may have different effects in different
populations.
For example, Co was associated with an increase in abdominal
fascia pigmentation in three stocks and with a decrease in three stocks,
presumably due to Tnteractions with the residual genotype.
Sex-linkedl
barring., B_j interacted with E_to reduce fascia pigment, but in the presence of
e + or e b melanization was increased.
A marked reduction in testes melanlzation was found for I when present with EE_;however, the effect was lo_t in
the presence
of e+ and eb.
""
I!
Unfortunately,
time does not permit a detailed look at all of the aspects
of the genetics of melanization.
It would be impossible to make the story
complete in any event because there is still much that we do not know.
In fact,
we are still isolating new mutations, and have just begun to appreciate the number
and complexities of genetic interactions responsible for the many variations in
phenotype.
I do feel that a good start has been made and hope that some time in
the future the completed story will be available°
-83-
REFERENCES
I.
Brumbaugh, J. A., 1967o
Differentiation
of black-red melanin in the fowl:
Interaction of pattern genes and feather follicle milieu.
J° Expero Zool. 166: 11-23.
2.
Brumbaugh, J. Ao, 1968o
Ultrastructural
differences between forming
eumelanin and pheomelanin as revealed by the pink-eye mutation in
the fowlo
Devel. Biol0 18:375-390o
3.
Brumbaugh, J. Ao, 1971. The ultrastructural
upon black-red melanin differentiation
24:392-412o
4.
Brumbaugh, J. Ao, R° Ro Bowers and Go Eo Chatterjee,
19730
Genotypesubstrate interactions altering Golgi development during melanogeneslso
Pigment Cell 1:47-54o
5.
Brumbaugh, Jo A., and Wo Fo Hollander, 1965o
A further
locus in the fowl.
Iowa State Jo Scio 40:51-64o
6.
Brumbaugh, Jo Ao, and Wo Fo Hollander, 1966o
Genetics of buff and related
color patterns in the fowl.
Poultry Scio 45:451-457.
7.
Cote, R0 So, 1976o A genetic
domestic fowlo
Master's
8.
Huntsman, G. M., Fo N. Jerome and E. So Snyer, 1959o The relationship between
plumage color phenotypes and the presence of black melanin In the abdomen
of broiler chickens: Study I. Poultry Scio 38:878-881o
9.
Huntsman, Go Mo, Fo No Jerome and Eo So Snyder, 1960o
The relationship between
plumage color phenotypes and the presence of black melanin in the abdomen
of broiler chickens: Study 2o Poultry Scio 39:882-886.
study of the E pattern
analysis of self-black plumage color
thesis, University of Massachusetts°
10.
Hurt, Fo Bo, 1949o
11o
Jaap, R. Go, 1958.
Black abdomen
in broiler chickens° Poultry
12.
Kimball, Eo, 1953a.
Genetics
Poultry Scio 32: 13-17o
of secondary
plumage
patterns
13.
Kimball, E., 1953b.
Genetics of Buttercup
Poultry Scio 32: 683-692°
plumage
pattern
14.
Kimball, Eo, 1954.
Genetics
Scio 33: 472-481o
15.
Kimball,
Eo, 1959.
Genetics
effects of the I and S loci
in the fowl.
Devel. Biolo
Barred
of the Fowlo
Book Co0,
Inco, New York.
- A pleiotropic effect of plumage
Scio 37:112-116o
of birchen
Hamburg
McGraw-Hill
in the
plumage
plumage
pattern
pattern°
color
genes
in the fowlo
in the fowlo
in the fowl.
Poultry
Scio
Poultry
38:224-225°
-84-
REFERENCES
16.
Kimball, Eo, 196Oa.
232-233°
Differential
penciled
17.
Kimball, E., 1960b.
233-234.
Genetic
18.
Kuit, A. R., 1967.
The relationship between some colour genotypes and
melanin in the abdomen of chickens.
Poultry Sci. 46: 1477-14!80.
19.
Lucas, Ao Mo, and Po R. Stettenheim, 1972o
Avian Anatomy.
Integument, Part
II. Agriculture Handbook 362. U.S. Govto Printing Office, Washington,
DoC., pp0 391-419.
20°
Malone, Go W., 1975. The influence of residual genotype on the expression
of silver and gold in the fowl.
Master's thesis, University of
Massachusetts.
21.
Malone, G. Wo, and J. R. Smyth, Jr., 1975ao
Chick down eumelanization
associated with the Columbian restriction pattern.
Poultry Sci.
54:1787
(Abst.)
22.
Malone, G. W., and J. R. Smyth, Jr., 1975b.
Genetic interactions affecting
the expression of silver and gold in the down.
Poultry Scl. 54:
1787 (Abst.).
,
23.
Maul, G., and J. Brumbaugh, 1971.
On the possible function of coated vesicles
in melanogenesis
of the regenerating fowl feather°
Jo Cell. Biol.
48: 41-48.
24.
Moore, J. W., and J. Ro Smyth, Jro, 1971. Melanotic:
enigma in the fowl0
J0 Hered. 62: 214-219.
25.
Moore, J. Wo, and J. R. Smyth, Jr., 1972a.
The genetic basis of the birchen
pattern of the domestic fowl.
Poultry Scio 51: 214-222o
26.
Moore, J0 W0, and J. Ro Smyth, Jr°, 1972bo
Genetic factors assoc!ated with
the plumage pattern of the Barred Fayouml.
Poultry Sci0 51: 1149-1156.
27.
Moore, J. W., and J. Ro Smyth, Jr., 1972c.
Inheritance of Silver-laced
Wyandotte plumage pattern.
Jo Hered.
63: 179-184o
28.
Morejohn, Go Vo, 195;5. Plumage
(Gallus gallus) and related
29.
Searle, A. Go, 1968.
Comparative
Lagos Press, London.
30.
Smyth, Jo R., Jr., 1965. Allelic relationship
black, wild type and brown plumage pattern
44: 89-98°
origin
phenotypes.
of penciled
Poultry
pattern.
Sci.
Poultry
39:
Scl. 39:
Key to a phenotyplc
color allelism in the Red Jungle Eowl
domestic forms.
Genetics 40: 519"530.
Genetics
of Coat
Colour
in Mammals.
il
of genes determining extended
in the fowl.
Poultry Sci.
-85-
REFERENCES
31.
Smyth, J. R., Jr., 1970.
Genetic basis for plumage
New Hampshire fowl.
J. Hered. 61: 280-283.
32.
Smyth, J. R., Jr., and R. G. Somes, Jr., 1965.
the Columbian feather pattern in the fowl.
33.
Somes, R. G., Jr., 1971.
Sci. 50: 1798-1801.
34.
Somes, R. G., Jr., and J. R. Smyth, Jr., 1966.
Feather eumelanin distribution variations in Buff Orpington, New Hampshire.and Rhode Island
Red breeds of fowl.
Poultry Sci. 45: 40-49.
35.
Wilkins, L. M., 1975. A study of the genetic factors associated with
the pigmentation of the shank, abdominal fascia and testes of the
fowl.
Master's thesis, University of Massachusetts.
Buff Brahma,
color
pattern
in the
A new gene determining
J. Hered.
56: 151-156.
an autosexing
of chicken.
Poultry
-86-
Dr. Jo Robert Smyth,
Jr.
-
"GENETIC
CONTROL
OF MELANIN
PIGMENTATION
IN THE FOWL."
E. Go BUSS:
What tester should be used to identify the EWh/eWhCo/Co
and gold lines which can be used for sexing by down color?
Jo Ro SMYTH,
JR.:
I think that the ideal tester would
silver
be a recessive
wheaten with a genetic malkeup of eY /eY co+ /co+ s+/s + (s+ /-).
The e_ permits
you to read the E-locus
since it is the most recessive E-allele.
Testcross
progeny that are eWh/eY'will, of course, have wheaten colored down°
if Co is
present in the testcross chick, then the pheomelanin will be oblous (compared to
the pure l_ght cream wheaten chick) in the presence of s+ /s + or s+ /-o
In the
silver line you can test your females against the same wheaten tester and look
for the silver-gold difference:
To test the male side it may be necessary
fix Co in S/s+ heterozygotes before making the line homozygous for So J'
to
I should also mention that when it is desirable to have one of the parent lines
homozygous for I/I, it is helpful to work with I/i+ while fixing the desired
genotype for sexing°
If the gold (male) line is dominant white, then one can
determine a great deal about eumelanin distribution
(Co, E-alleles, ere!o) by
visibly examining the I/i individual°
Once a workable sexing genotype is
present then it is a simple matter to make the line I/Io
Bo Co WENTWORTH:
Is it possible to utilize the sex-linked silver and gold
alleles in chicks heterozygous for E?
in other words, could you use a White
Leghorn that was I/IE/E as one parent?
Jo Ro SMYTH, JR°:
I don't believe that this type of bird can be u:sed, but
we haven't really looked into this approach°
We snow S and s+ would not be
expressed in the eumelanized down°
A gene like Db modifies black down Iresulting
in a dark brown color; however, S and s+ are not expressed on this typeiof down
either°
However, I would not want to say that some combination of Columbianlike modifiers including Co might not make sexing with E possibleo
Eo Go BUSS:
Do I understand you correctly in that you have not been considering the alleles at the sex-linked barring locus?
Jo Ro SMYTH, JR.:
All of our work with S-alleles has been done in the
presence of b+o We have not encountered the partial albinism mutation, but we
have made observations on effects of barring (b) on testcross offspring
Since
B d_lutes down pigmentation,
it makes interpretation of testcross progeny
difficult.
Therefore, we have preferred to work in its absence, since we were
using the sex-linked S-Iocuso
Even though B often has a hlgh gene frequency in
populations with white plumage, it is less confusing to eliminate it unless you
plan to use it as the sexing agent°
Barring does
dilution effect, but this might be hard to follow
have a significant
in an I/iT chick°
dosage