Opaline budgerigar mutation
Encyclopedia
The Opaline budgerigar mutation is one of approximately 30 mutations affecting the colour or appearance of budgerigar
s. It is the underlying mutation of the Opaline variety. When combined with the Yellowface II
and Clearwing
mutations the Rainbow variety is produced.
In the non-Opaline the wings show dark grey or black markings over a yellow or white ground, but in the Opaline the ends of the barbs
of the wing coverts
assume the same colour as the body, rather than the ground colour. This suffusion of body colour in the wings produces the opalescent effect which gave the mustation its name. The area of black pigmentation in each feather is reduced and in the original specimens the wing butts were particularly devoid of black pigment, resulting in a clear area often called the 'thumb-print'. These thumb-prints appear to be associated with a clear 'V', but are now seen less often, since the Budgerigar Standard calls for normal wing markings in the Opaline.
The flight feather
s of the budgerigar consist of 10 primaries
and 10 secondaries
. These are dark grey with a clear central band across every feather from the 2nd primary to the 8th secondary. These clear areas are not visible in the folded wing, but form a prominent continuous band running right along the wing when it is stretched out. It is hidden from above by the coverts but is visible from beneath. In the Opaline this clear band is present on every flight feather and is much broader. Only the distal half of the flight feather is dark, with the clear zone extending from the mid-point to the shaft. Because it is broader it is visible in the primaries of the folded wing of the Opaline, just beneath the secondaries and primary wing coverts, as a small clear patch.
A similar effect occurs in all the wing feathers, most noticeably in the primary and secondary wing coverts, and also in the six tail feathers, which carry a similar clear band on feathers 2 to 6 in the non-Opaline. The first (longest) tail feather of the Opaline also carries a rather blotchy clear area of somewhat variable extent, and the suffusion of body colour present to a small degree in the non-Opaline is intensified in the Opaline.
Most Opalines show a brighter body colour than the corresponding non-Opaline, paricularly in nest feather and particularly in the rump area. This is due to a reduction in the melanin content of the barbules
of the contour feathers
.
The final characteristic of the Opaline (and the Cinnamon
) is the colour of the down feathers of the young nestling. These are white instead of the usual grey, and this allows Opalines to be identified at a very early age.
, Scotland, bred what was described as a 'pied' Cobalt hen from a perfectly normal Skyblue cock and Mauve hen. The parents came from a strain kept locally which had never produced anything unusual, and Mr Brown bred no more than the one mutant, even though the same pair bred many Cobalts in both 1933 and 1935.
Towards the end of 1933 Mr and Mrs Ashby of nearby Ayr
purchased this 'pied' Cobalt, which they described as being "exceptionally large with a fine head and most excellent spots", although both parents were quite mediocre. The mutant's peculiarities were that the head, neck and nape were almost pure white with slight markings in places and nearly all the flight feathers, primaries
and secondaries
, were edged with cobalt in place of white, making the bird almost a 'Cobalt-wing'. The mutant was not a pied of any of the present-day types (these were not established in 1933), but an Opaline, although the variety was not to be known by that name until a few years later.
In 1934 the Ashby's paired the mutant hen to a quality Light Green split blue cock and Skyblues, Light Greens and a Dark Green of a perfectly normal appearance were bred. In 1935 one of the Skyblue cocks was mated back to the mutant hen, and the very first nest produced two Opaline Cobalt cocks and an Opaline Skyblue hen. The Opaline mutation had been fixed.
Early in 1936 circumstances forced the Ashby's to dispose of all their Opalines, which at that time were known as 'Marbled', and the entire stock, with the exception of two pairs which went to Andy Wilson of Glasgow
, went to Walter Higham of Blackburn, under the care of his aviary manager, Len Hillas. From these two studs came the vast majority of British Opalines, most of them carrying the wide head and large spots which first caught the attention of the Ashby's.
In Australia, also around 1933 (the exact date is uncertain), Mr S E Terrill discovered a mutant budgerigar, a Light Green hen in nest feather, among thousands of wild birds caught by trappers and sent to Adelaide
market. He bought her, and described her special features as "... almost complete absence of barring on the back of the neck and mantle and its replacement by the body colour ... the mask being extended back, covering the top of the head ... the bars on the wing coverts
reduced in number and intensity, their yellow margins being greatly enlarged and nuch suffused in green."
Mr Terrill, who lived near Adelaide, paired the hen to a Blue Silver (the Australian name at the time for the variety now known as Dilute Skyblue or White
) and bred three cocks and a hen in 1934, all Light Green in appearance. About November 1935 the three cocks were paired up, one to a Cinnamon Light Green, one to a Cobalt and one to his mother. The first two pairings produced six Opalines, all hens, and the third several Opalines, both cocks and hens. The name 'Opaline' was suggested in 1936 by Mr R J Byfield of Hobart
, Tasmania, on being particularly impressed by the vividness of colour shown by these young birds in nest feather. Mr Terrill adopted the name and after he suggested it in the Budgerigar Bulletin in September 1936 it rapidly gained universal acceptance throughout the world.
But maybe neither Mr Brown nor Mr Terrill were the first to breed an Opaline. In 1962 Mr J Riley of Yorkshire wrote, "In 1930 or 1931 a pair of my Light Greens produced a chick that was of good size and type with mask and spots that were a living dream; the only snag was that its wings were mismarked and grizzled, these markings extending over the bird's back." Mr Riley kept the bird and used it to try to improve the spots of his Light Greens, but further 'mis-marked' birds appeared. He disposed of them all soon afterwards and only a long time later did he see Opalines and realise that he had bred them first and cast them aside.
The Opaline appeared yet again in 1935, in the aviaries of L Raymaekers in Brussels
. Mr Higham imported two Opaline Mauve cocks and one Opaline Greywing Mauve hen from Mr Raymaekers in 1937 and Cyril Rogers confirmed they were the same mutation as the Scottish one, although their wing barring seemed noticeably lighter.
, the locus
of its gene
being carried on the X chromosome
. It is recessive
to wild-type. The gene locus has the symbol op. The wild-type allele
at this locus is notated op+ and the Opaline allele is notated op.
In birds, the cock has two X chromosomes and the hen has one X and one Y chromosome. So in hens whichever allele is present on the single X chromosome is fully expressed in the phenotype
. Hens cannot be split for Opaline (or any other sex-linked mutation). In cocks, because Opaline is recessive, the Opaline allele must be present on both X chromosomes (homozygous) to be expressed in the phenotype. Cocks which are heterozygous for Opaline are identical to the corresponding Normal. Such birds are said to be split for Opaline, usually written '/opaline'.
The table on the right shows the appearance of all possible genetic combinations involving the Opaline mutation.
The Opaline gene is linked
to other genes located on the X chromosome, i.e. to the genes of other sex-linked mutations. These sex-linked mutations include the Cinnamon
and Slate
mutations and the two allelic mutations at the ino locus -- the Ino
and the Sex-linked Clearbody
. The cross-over
or recombination
values between Opaline and these linked genes has not been measured accurately, but results collected by C Warner and T Daniels found 41 crossovers in 113 between Cinnamon and Opaline, giving a recombination ratio of 36±6%. Since the ino locus is known to be very close to the cin locus, the recombination ratio between Opaline and both Ino and Sex-linked Clearbody must also be around 36%. The opinion has been expressedthat there is a close link between Opaline and Slate.
Cocks split for both Cinnamon and Opaline have one Cinnamon allele and one Opaline allele together with one each of the corresponding wild-type alleles. The linkage between the Cinnamon and Opaline genes gives rise to two types of split cinnamon-opaline cocks, both visually identical.
Hens cannot be split for any sex-linked gene, so only cocks exist in Type I and Type II form.
Budgerigar
The Budgerigar , also known as Common Pet Parakeet or Shell Parakeet informally nicknamed the budgie, is a small, long-tailed, seed-eating parrot, and the only species in the Australian genus Melopsittacus...
s. It is the underlying mutation of the Opaline variety. When combined with the Yellowface II
Yellowface II budgerigar mutation
The Yellowface II budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. In combination with the Blue, Opaline and Clearwing mutations, the single factor Yellowface II mutation produces the variety called Rainbow....
and Clearwing
Clearwing budgerigar mutation
The Clearwing budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Clearwing variety, often known as Yellowwings in the green series and Whitewings in the blue series. When combined with the Greywing mutation the...
mutations the Rainbow variety is produced.
Appearance
The Opaline mutation is characterised by several features which are invariably present, although many show variations in the intensity of their expression. The most obvious effect is on the striations which extend from the top of the head down the neck to between the wings in the non-Opaline. In the Opaline these striations are very much reduced in intensity, being almost absent in many individuals, particularly in small birds of yellow (as opposed to buff) feather. The cap of the Opaline extends further back over the top of the head, gradually merging into an area the same colour as the body which continues down the back of the head to form a 'V' shape between the wings. The intensity of the striations in this area is variable, but in the original mutations, particularly the Australian, the 'V' was very clear.In the non-Opaline the wings show dark grey or black markings over a yellow or white ground, but in the Opaline the ends of the barbs
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
of the wing coverts
Covert (feather)
A covert feather on a bird is one of a set of feathers, called coverts, which as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail.- Wing-coverts :...
assume the same colour as the body, rather than the ground colour. This suffusion of body colour in the wings produces the opalescent effect which gave the mustation its name. The area of black pigmentation in each feather is reduced and in the original specimens the wing butts were particularly devoid of black pigment, resulting in a clear area often called the 'thumb-print'. These thumb-prints appear to be associated with a clear 'V', but are now seen less often, since the Budgerigar Standard calls for normal wing markings in the Opaline.
The flight feather
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
s of the budgerigar consist of 10 primaries
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
and 10 secondaries
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
. These are dark grey with a clear central band across every feather from the 2nd primary to the 8th secondary. These clear areas are not visible in the folded wing, but form a prominent continuous band running right along the wing when it is stretched out. It is hidden from above by the coverts but is visible from beneath. In the Opaline this clear band is present on every flight feather and is much broader. Only the distal half of the flight feather is dark, with the clear zone extending from the mid-point to the shaft. Because it is broader it is visible in the primaries of the folded wing of the Opaline, just beneath the secondaries and primary wing coverts, as a small clear patch.
A similar effect occurs in all the wing feathers, most noticeably in the primary and secondary wing coverts, and also in the six tail feathers, which carry a similar clear band on feathers 2 to 6 in the non-Opaline. The first (longest) tail feather of the Opaline also carries a rather blotchy clear area of somewhat variable extent, and the suffusion of body colour present to a small degree in the non-Opaline is intensified in the Opaline.
Most Opalines show a brighter body colour than the corresponding non-Opaline, paricularly in nest feather and particularly in the rump area. This is due to a reduction in the melanin content of the barbules
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
of the contour feathers
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
.
The final characteristic of the Opaline (and the Cinnamon
Cinnamon budgerigar mutation
The Cinnamon budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Cinnamon variety and, with Ino, a constituent mutation of the Lacewing variety.- Appearance :...
) is the colour of the down feathers of the young nestling. These are white instead of the usual grey, and this allows Opalines to be identified at a very early age.
Historical Notes
In 1933 Mr A Brown of KilmarnockKilmarnock
Kilmarnock is a large burgh in East Ayrshire, Scotland, with a population of 44,734. It is the second largest town in Ayrshire. The River Irvine runs through its eastern section, and the Kilmarnock Water passes through it, giving rise to the name 'Bank Street'...
, Scotland, bred what was described as a 'pied' Cobalt hen from a perfectly normal Skyblue cock and Mauve hen. The parents came from a strain kept locally which had never produced anything unusual, and Mr Brown bred no more than the one mutant, even though the same pair bred many Cobalts in both 1933 and 1935.
Towards the end of 1933 Mr and Mrs Ashby of nearby Ayr
Ayr
Ayr is a town and port situated on the Firth of Clyde in south-west Scotland. With a population of around 46,000, Ayr is the largest settlement in Ayrshire, of which it is the county town, and has held royal burgh status since 1205...
purchased this 'pied' Cobalt, which they described as being "exceptionally large with a fine head and most excellent spots", although both parents were quite mediocre. The mutant's peculiarities were that the head, neck and nape were almost pure white with slight markings in places and nearly all the flight feathers, primaries
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
and secondaries
Flight feather
Flight feathers are the long, stiff, asymmetrically shaped, but symmetrically paired feathers on the wings or tail of a bird; those on the wings are called remiges while those on the tail are called rectrices . Their primary function is to aid in the generation of both thrust and lift, thereby...
, were edged with cobalt in place of white, making the bird almost a 'Cobalt-wing'. The mutant was not a pied of any of the present-day types (these were not established in 1933), but an Opaline, although the variety was not to be known by that name until a few years later.
In 1934 the Ashby's paired the mutant hen to a quality Light Green split blue cock and Skyblues, Light Greens and a Dark Green of a perfectly normal appearance were bred. In 1935 one of the Skyblue cocks was mated back to the mutant hen, and the very first nest produced two Opaline Cobalt cocks and an Opaline Skyblue hen. The Opaline mutation had been fixed.
Early in 1936 circumstances forced the Ashby's to dispose of all their Opalines, which at that time were known as 'Marbled', and the entire stock, with the exception of two pairs which went to Andy Wilson of Glasgow
Glasgow
Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...
, went to Walter Higham of Blackburn, under the care of his aviary manager, Len Hillas. From these two studs came the vast majority of British Opalines, most of them carrying the wide head and large spots which first caught the attention of the Ashby's.
In Australia, also around 1933 (the exact date is uncertain), Mr S E Terrill discovered a mutant budgerigar, a Light Green hen in nest feather, among thousands of wild birds caught by trappers and sent to Adelaide
Adelaide
Adelaide is the capital city of South Australia and the fifth-largest city in Australia. Adelaide has an estimated population of more than 1.2 million...
market. He bought her, and described her special features as "... almost complete absence of barring on the back of the neck and mantle and its replacement by the body colour ... the mask being extended back, covering the top of the head ... the bars on the wing coverts
Covert (feather)
A covert feather on a bird is one of a set of feathers, called coverts, which as the name implies, cover other feathers. The coverts help to smooth airflow over the wings and tail.- Wing-coverts :...
reduced in number and intensity, their yellow margins being greatly enlarged and nuch suffused in green."
Mr Terrill, who lived near Adelaide, paired the hen to a Blue Silver (the Australian name at the time for the variety now known as Dilute Skyblue or White
Dilute budgerigar mutation
The Dilute budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is one of the constituent mutations of several recognised varieties: the Light, Dark, Olive, Grey and Suffused Yellows and the Grey and Suffused Whites....
) and bred three cocks and a hen in 1934, all Light Green in appearance. About November 1935 the three cocks were paired up, one to a Cinnamon Light Green, one to a Cobalt and one to his mother. The first two pairings produced six Opalines, all hens, and the third several Opalines, both cocks and hens. The name 'Opaline' was suggested in 1936 by Mr R J Byfield of Hobart
Hobart
Hobart is the state capital and most populous city of the Australian island state of Tasmania. Founded in 1804 as a penal colony,Hobart is Australia's second oldest capital city after Sydney. In 2009, the city had a greater area population of approximately 212,019. A resident of Hobart is known as...
, Tasmania, on being particularly impressed by the vividness of colour shown by these young birds in nest feather. Mr Terrill adopted the name and after he suggested it in the Budgerigar Bulletin in September 1936 it rapidly gained universal acceptance throughout the world.
But maybe neither Mr Brown nor Mr Terrill were the first to breed an Opaline. In 1962 Mr J Riley of Yorkshire wrote, "In 1930 or 1931 a pair of my Light Greens produced a chick that was of good size and type with mask and spots that were a living dream; the only snag was that its wings were mismarked and grizzled, these markings extending over the bird's back." Mr Riley kept the bird and used it to try to improve the spots of his Light Greens, but further 'mis-marked' birds appeared. He disposed of them all soon afterwards and only a long time later did he see Opalines and realise that he had bred them first and cast them aside.
The Opaline appeared yet again in 1935, in the aviaries of L Raymaekers in Brussels
Brussels
Brussels , officially the Brussels Region or Brussels-Capital Region , is the capital of Belgium and the de facto capital of the European Union...
. Mr Higham imported two Opaline Mauve cocks and one Opaline Greywing Mauve hen from Mr Raymaekers in 1937 and Cyril Rogers confirmed they were the same mutation as the Scottish one, although their wing barring seemed noticeably lighter.
Genetics
The Opaline mutation is sex-linkedSex linkage
Sex linkage is the phenotypic expression of an allele related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of inheritance...
, the locus
Locus (genetics)
In the fields of genetics and genetic computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
of its gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
being carried on the X chromosome
X chromosome
The X chromosome is one of the two sex-determining chromosomes in many animal species, including mammals and is common in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system...
. It is recessive
Recessive
In genetics, the term "recessive gene" refers to an allele that causes a phenotype that is only seen in a homozygous genotype and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father...
to wild-type. The gene locus has the symbol op. The wild-type allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
at this locus is notated op+ and the Opaline allele is notated op.
| Sex | Genotype | Phenotype |
|---|---|---|
| Cocks | op+/op+ | Normal |
| op+/op | Normal (/opaline) | |
| op/op | Opaline | |
| Hens | op+/Y | Normal |
| op/Y | Opaline |
In birds, the cock has two X chromosomes and the hen has one X and one Y chromosome. So in hens whichever allele is present on the single X chromosome is fully expressed in the phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
. Hens cannot be split for Opaline (or any other sex-linked mutation). In cocks, because Opaline is recessive, the Opaline allele must be present on both X chromosomes (homozygous) to be expressed in the phenotype. Cocks which are heterozygous for Opaline are identical to the corresponding Normal. Such birds are said to be split for Opaline, usually written '/opaline'.
The table on the right shows the appearance of all possible genetic combinations involving the Opaline mutation.
The Opaline gene is linked
Genetic linkage
Genetic linkage is the tendency of certain loci or alleles to be inherited together. Genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis, and are thus genetically linked.-Background:...
to other genes located on the X chromosome, i.e. to the genes of other sex-linked mutations. These sex-linked mutations include the Cinnamon
Cinnamon budgerigar mutation
The Cinnamon budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Cinnamon variety and, with Ino, a constituent mutation of the Lacewing variety.- Appearance :...
and Slate
Slate budgerigar mutation
The Slate budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Slate variety.- Appearance :...
mutations and the two allelic mutations at the ino locus -- the Ino
Ino budgerigar mutation
The Ino budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Albino and Lutino varieties and, with Cinnamon, a constituent mutation of the Lacewing variety.- Appearance :...
and the Sex-linked Clearbody
Sex-linked Clearbody budgerigar mutation
The Sex-linked Clearbody budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Texas Clearbody variety....
. The cross-over
Genetic linkage
Genetic linkage is the tendency of certain loci or alleles to be inherited together. Genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis, and are thus genetically linked.-Background:...
or recombination
Genetic recombination
Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...
values between Opaline and these linked genes has not been measured accurately, but results collected by C Warner and T Daniels found 41 crossovers in 113 between Cinnamon and Opaline, giving a recombination ratio of 36±6%. Since the ino locus is known to be very close to the cin locus, the recombination ratio between Opaline and both Ino and Sex-linked Clearbody must also be around 36%. The opinion has been expressedthat there is a close link between Opaline and Slate.
Cocks split for both Cinnamon and Opaline have one Cinnamon allele and one Opaline allele together with one each of the corresponding wild-type alleles. The linkage between the Cinnamon and Opaline genes gives rise to two types of split cinnamon-opaline cocks, both visually identical.
- Type I split cinnamon-opalines cocks are bred by mating Cinnamon-Opalines to Normals and have the two mutant alleles on the same chromatidChromatidA chromatid is one of the two identical copies of DNA making up a duplicated chromosome, which are joined at their centromeres, for the process of cell division . They are called sister chromatids so long as they are joined by the centromeres...
, symbolised as cin+-op+/cin-op. Geneticists call this 'couplingGenetic linkageGenetic linkage is the tendency of certain loci or alleles to be inherited together. Genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis, and are thus genetically linked.-Background:...
' rather than 'Type I'. Because of the linkage, the Cinnamon and Opaline alleles from Type I cocks tend to be inherited together in their progeny. When mated to Normal hens, Type I cocks produce predominantly Cinnamon-Opaline and Normal hens, with Cinnamon and Opaline hens resulting rarely from a cross-over. Roughly one third of the hens will be Cinnamon-Opaline, one third Normal, one sixth Cinnamon and one sixth Opaline.
- Type II split cinnamon-opaline cocks are bred by mating Cinnamons to Opalines and have the Cinnamon and Opaline mutant alleles on opposite chromatids, symbolised as cin+-op/cin-op+. Geneticists call this 'repulsionGenetic linkageGenetic linkage is the tendency of certain loci or alleles to be inherited together. Genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis, and are thus genetically linked.-Background:...
' rather than 'Type II'. Because of the separation, the Cinnamon and Opaline alleles from Type II birds tend to be inherited separately in their progeny. When mated to Normal hens, Type II cocks produce predominantly Cinnamon and Opaline hens, with Cinnamon-Opaline and Normal hens resulting rarely from cross-overs. Roughly one third of the hens will be Cinnamon, one third Opaline, one sixth Cinnamon-Opaline and one sixth Normal.
Hens cannot be split for any sex-linked gene, so only cocks exist in Type I and Type II form.