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          The violet factor works in a manner, similar to the dark factor. With the exception of visual violets the violet factor does not produce an actual colour, instead it modifies the shade of the pre-existing colour.

          There is still some doubt about the location for the violet factor locus. Some authors believe the chromosome that carries the dark factor also carries the violet factor, originating linkage between these loci. Other authors believe the segregation of the two factors is independent. But for now, this matter will not be further discussed.

          The wild-type allele or normal allele for the violet factor, V+, does not change the colour or shade of a bird. Most normal budgerigars are homozygous (double factor) for the wild-type allele. The mutated allele, the true violet factor, V, is the one responsible for visual violets and darker shades.

Symbols for allelomorphs

(according to Mutavi)

Gene type

Effect of the allelomorphs that control melanin production

 

V+

Wild-type

Does not change the pre-existing colour

V

Mutant

Changes the pre-existing colour

Table 9 – Symbols and visual effect of the individual allelomorphs for the violet factor

          There is great discussion about the inheritance pattern involving the V+ and V alleles. Some articles classify the V allele as dominant over the V+ allele. This interpretation is not supported, however, by an increasing number of studies, showing that the V+ and V alleles are, in fact, incomplete dominant. During the next paragraphs I will pursue the incomplete dominance point of view.

Genotype

Phenotype

Pre-existing colour

Locus for the violet factor

Locus for

Melanin production

Locus for yellow pigment production

Locus for the dark factor

dil+ dil+

bl+ bl+

D+ D+

V+ V+

Light green

dil+ dil+

bl+ bl+

D+ D

V+ V+

Dark green

dil+ dil+

bl+ bl+

D+ D+

V+ V

Dark green

dil+ dil+

bl+ bl+

D D

V+ V+

Olive green

dil+ dil+

bl+ bl+

D+ D

V+ V

Olive green

dil+ dil+

bl+ bl+

D+ D+

V V

?

 

 

 

 

 

dil+ dil+

bl bl

D+ D+

V+ V+

Sky blue

dil+ dil+

bl bl

D+ D

V+ V+

Cobalt (blue)

dil+ dil+

bl bl

D+ D+

V+ V

Cobalt (blue)

dil+ dil+

bl bl

D D

V+ V+

Mauve (blue)

dil+ dil+

bl bl

D+ D

V+ V

Visual violet

dil+ dil+

bl bl

D+ D+

V V

Visual violet

Table 10 – Visual effect of the locus for the violet factor over the pre-existing colour

          On green series birds, the addition of one mutant allele, V, implicates the bird will suffer an increase on colour depth. A single violet factor light green budgerigar is very similar to a normal dark green while a single violet factor dark green becomes a visual olive green. Genetically, the former bird is of light shade while the later is of medium shade but visually they are one step up on the colour depth ladder.

          The addition of one violet factor to genetically sky blue birds produces visual cobalts. On genetically medium shade blue birds (cobalts), one violet factor originates visual violets. The interaction between one dark factor, D, plus one violet factor on blue birds is one way to produce visual violets but it is not the only one. Double violet factor cobalts are also visual violets and, perhaps the most unexpected of all violets is the double violet factor sky blue. The presence of one dark factor is not essential for the violet colour to arise.

          Identification of single violet factor sky blues is possible. Observed under natural light they look very much like normal cobalts, with the exception of the flight feathers and the two long tail feathers that are violet at the quill end darkening to navy blue towards the tip. Normal cobalts have navy blue flight feathers and tails.

          Distinction between single violet factor cobalts and double violet factor sky blue budgerigars is also possible. They are both visual violets but the flight feathers of violet cobalts have a dark shade of blue while double violet factor sky blues have violet flight feathers and violet tail feathers at the quill end darkening to navy blue towards the other end.

          Double violet factor cobalts show a stronger violet shade but show no other significant differences from single violet factor cobalts.

          Single violet factor sky blues and single violet factor light greens are visually medium shade but genetically they are light shade. The violet factor may add to colour depth but not in the same way the dark factor does.

          As we seen earlier, the dark factor modifies the structure of the feather cells. The mutant violet factor, in turn, increases the concentration of melanin at the medulla core. The more melanin feathers produce, the greater becomes capacity to absorb light at the blue end of the spectrum. After the blue radiation has been absorbed, all that's left is the violet radiation. Having no yellow pigment production, blue birds appear violet.

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Home | Introduction | Notions on genetics | Two distinct loci and the colour pigments | Colour depth | The violet factor
Sex-linked colours | Linkage between different loci | Mendel's Chart
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