Dilute Budgerigar Mutation
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The Dilute budgerigar mutation is one of approximately 30 mutations affecting the colour of
budgerigar The budgerigar ( ; ''Melopsittacus undulatus''), also known as the common parakeet or shell parakeet, is a small, long-tailed, seed-eating parrot usually nicknamed the budgie ( ), or in American English, the parakeet. Budgies are the only spe ...
s. 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.


Appearance

The Dilute mutation changes the body colour of the wild-type Light Green to yellow, with a variable amount of light green suffusion. The suffusion is deepest on the rump and around the vent. The spots and markings on the wing, head and neck, which are black in the wild-type, are pale grey. The cheek patches are pale lavender and the long tail feathers are pale bluey-grey. The eyes remain normal, with white irises when adult. There is considerable variation in the intensity of the green suffusion, but the best exhibition birds of the 1930s showed very little and also had very faint wing markings. These are the Dilute Light Greens, usually known as Light Yellows. The green suffusion becomes progressively darker when single and double factors of the Dark mutation are present. These are the Dilute Dark Greens and Dilute Olives, usually known as Dark and Olive Yellows. When the suffusion is particularly heavy the bird is known as a Suffused Yellow. In the blue series the absence of the yellow pigment turns the body colour to white, although this is usually suffused with blue, often quite heavily. When the suffusion is light, Dilute Skyblues are known as Whites; when it is heavy they are known as Suffused Whites. Dilute Cobalts and Mauves are usually known as Suffused Whites.


Historical notes

Budgerigars were first introduced into Europe by the ornithologist and bird artist,
John Gould John Gould (; 14 September 1804 – 3 February 1881) was an English ornithologist. He published a number of monographs on birds, illustrated by plates produced by his wife, Elizabeth Gould, and several other artists, including Edward Lear, ...
, in 1840, when he imported to England a pair which had been bred by his brother-in-law, Charles Coxon.Watmough (1951), p13 They grew steadily in popularity. For the first thirty years of their domestication only the wild-type Light Green budgerigar was known, but in 1872 birds with greenish-yellow bodies and very pale wing markings were reported from Belgium (in both
Brussels Brussels (french: Bruxelles or ; nl, Brussel ), officially the Brussels-Capital Region (All text and all but one graphic show the English name as Brussels-Capital Region.) (french: link=no, Région de Bruxelles-Capitale; nl, link=no, Bruss ...
and
Antwerp Antwerp (; nl, Antwerpen ; french: Anvers ; es, Amberes) is the largest city in Belgium by area at and the capital of Antwerp Province in the Flemish Region. With a population of 520,504,
) and Germany (in both
Kassel Kassel (; in Germany, spelled Cassel until 1926) is a city on the Fulda River in northern Hesse, Germany. It is the administrative seat of the Regierungsbezirk Kassel and the district of the same name and had 201,048 inhabitants in December 2020 ...
and
Berlin Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...
). This, now known as the Dilute mutation, was the first mutation observed in the domesticated budgerigar. Joseph Abrahams obtained some of these new yellow birds from Belgium and bred the first Yellow, as it was called, in Great Britain in 1884. These strains, in both Britain and Europe, laid the foundations for the very popular exhibition Light Yellow of the 1920s and 30s, which were often known by the alternative names of Buttercups or Buttercup Yellows. The popularity of the variety declined after the Lutino became available in the late 1930s. In 1896, George Keartland of the Calvert Expedition to the
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data
of
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, observed a yellow budgerigar flying wild in a flock on three occasions. This suggests the Dilute mutation is relatively common in
heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
form among the wild populations, as two such heterozygous individuals would need to mate in order to produce a visible Dilute. Although the Blue mutation was first seen soon after the first Dilutes, in 1878, and had become established by 1890 in Europe, the first combination of the Blue and Dilute mutations in double
homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
form did not appear until around 1920, some 30 to 40 years later. This combination was the White (known as Silver in Australia), and it was first bred in England by H D Astley in September 1920 from a pair of Skyblues. A White was also reported in Paris in the same year. Whites were never as popular as the Yellows, as it was much harder to approach the exhibition ideal of a pure white bird.


Genetics

The Dilute mutation is recessive to its wild-type
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
, so a bird possessing a single Dilute allele (the
heterozygote Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
) is identical in appearance to the wild-type Light Green. That is, the presence of a single wild-type allele is sufficient to permit the production of the normal number of
melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
granules. Among the budgerigar fancy such a bird is said to be a Light Green split dilute, usually written Light Green/dilute, although Light Green/yellow has been used.Taylor and Warner (1986) In a bird which has two Dilute alleles (the
homozygote Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
) the number of melanin granules is greatly reduced, to around 5% of the normal amount. This results in a much reduced intensity of the black markings, and less absorption of light which passes through the cloudy layer in the
medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...
of barbs. As this absorption of light is a necessary part of the process which generates the blue colouration the intensity of blue is also greatly reduced. The Dilute mutation is one of a series of multiple alleles at the same
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award' ...
, called ''dil+'' in the wild-type. The others are the Clearwing (''dilcw'') and Greywing (''dilgw'') mutations. The Dilute allele (''dild'') is recessive to all other alleles at this locus, so for the Dilute character to be expressed in the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
the
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
must be homozygous for this allele.


Notes


References

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External links


World Budgerigar Organisation (WBO)


{{Budgerigar mutations Budgerigar colour mutations