Make your own free website on Tripod.com

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

Chat | Forum | FAQ's | Downloads | Links | Mailing List | E-mail me

  


          Different varieties of budgerigars show combinations of four different colours: green, blue, yellow and white.

          On the feathers and skin of budgerigars two types of pigment are produced: melanin and yellow pigments.

          Melanin is a black or dark brown oval pigment. Strong deposits of this pigment are visible on the wing markings. Smaller deposits of melanin on the body feathers are co-responsible for the production of the blue colour. The process by which melanin is though to co-produce blue radiation is subjected to some discussion. The optical effect called Tyndall's phenomenon was a first attempt to explain the existence of blue birds.

          More recently, another explanation based on an interference of light phenomenon was put forward. Basically, what causes the appearance of the blue colour is an absorption by melanin, of the radiation from the red end of the visible spectrum.

          The blue end of the spectrum escapes absorption, and is reflected back becoming visible to the observer.

          Yellow pigments (or psittacin) constitute another group of pigments, responsible for the production of the yellow colour.

          When, on the feathers of a bird, both types of pigment exist, the yellow pigments act like a filter over the blue radiation and the light that reaches the observer's eyes is green. A bird that only produces melanins is blue, while another that only produces yellow pigments is yellow. In the absence of both pigment types the bird is white.

          On a green bird the face is yellow because melanin production on this area does not occur but yellow pigments are produced. Similarly, on a blue bird the face is white because on this area no colour pigments occur.

          Each budgerigar has two different loci on different chromosome pairs that control the presence or absence of colour pigments. One locus controls melanin production while the other controls yellow pigment production.

          The locus for melanin production carries not only the wild-type gene, dil+, but also the mutations suffered by this gene throughout the generations. The wild-type gene determines production of melanin on the wings and body of a bird, to its maximum extent. This means the wings will show their characteristic black markings and the body feathers will reflect blue light.

          The mutations obtained from the original gene are the ones for greywing, dilgw, clearwing, dilcw and dilute, dil. All four allelomorphs affect the distribution of melanin on the wings or body.

          On greywings, the most visible effect is the reduction of melanin intensity on the wing markings. The production of melanin on the body is also reduced resulting on a paler body colour.

          On clearwings the reduction of the wing markings intensity is even more remarkable but the production of melanin on the body is almost not disturbed.

          The dilute gene produces an interesting distribution of melanin. It eliminates melanin from certain areas of the wings and body. Thus, wing markings and body colour become irregularly distributed. The intensity of colour on the areas where melanin production still occurs is similar to normal birds.

 

Symbols for allelomorphs (according to Mutavi)

Gene type

Effect of the allelomorphs that control melanin production

 

dil+

Wild-type

Black wing markings. Full blue light reflection.

dilgw

Mutant

Grey wing markings. Greatly reduced blue light reflection.

dilcw

Mutant

Lack of wing markings. Full blue light reflection.

dil

Mutant

Irregular black wing markings. Irregular blue light reflection.

Table 1 – Symbols and visual effect of the allelomorphs that occupy the "melanin production locus"

          The wild-type gene is dominant to any mutant form it is paired to. This way, a bird can be visually normal and split greywing, or split clearwing or split dilute.

          The allelomorphs for greywing and clearwing are incomplete dominant. A bird heterozygous for these two genes shows wing coloration typical of a greywing and body colour of a clearwing. Such a bird cannot be split for any of the two allelomorphs because both have a visible effect on the phenotype.

          Greywing is dominant to dilute. A bird can be visually greywing and split dilute.

          Clearwing is dominant to dilute. A bird can be visually clearwing and split dilute.

          Dilute is the most recessive of the allelomorphs; a visual dilute must be homozygous for this gene.

          The hierarchy among the allelomorphs is as follows: dil+ > dil

 gw = dil cw > dil.

 

Genotype

Effect of the locus that controls melanin production

 

dil+ dil+

 

Black wing markings.

Full blue light reflection.

 

dil+ dilgw

dil+ dilcw

dil+ dil

dilgw dilgw

Grey wing markings.

Greatly reduced blue light reflection.

dilgw dil

dilgw dilcw

Grey wing markings. Full blue light reflection.

dilcw dilcw

Lack of wing markings.

Full blue light reflection.

dilcw dil

dil dil

Irregular black wing markings. Irregular blue light reflection.

Table 2 – Visual effect of the pairs of allelomorphs that occupy the "melanin production locus"

          The locus responsible for yellow pigment production carries the allelomorphs associated with this pigment.

          The wild-type gene, bl+, determines a uniform production of yellow pigment over the wings, body and face of the bird.

          The mutation, bl1, determines that no yellow pigment production occurs. It is often called the "blue gene".

          The so-called yellowface mutation (or yellow face mutant I), bl2, is in fact, a gene that causes the elimination of yellow pigment. The bl2 gene is incorrectly called a "yellowface gene" because, in fact, it produces exactly the same effect than the bl1 gene. They are both "blue genes". It is only when the bl1 and the bl2 allelomorphs are combined on the same bird that a visual yellowface appears. Both genes are necessary to produce this type of visual yellowface bird. Because this kind of visual yellowface does not have any true yellowface genes it is also a called creamface budgerigar.

          The goldenface, blgf and yellowface mutant II, blyf2, are true "yellowface genes". They are yellow pigment production genes. The difference between the two genes is that blgf produces a stronger concentration of yellow pigment on the face of the bird, resulting on a richer shade of yellow while blyf2 produces a moderate concentration of this pigment, resulting on a slightly paler shade of yellow.

Symbols for allelomorphs (not according to Mutavi)

Gene type

Effect of the allelomorphs that control yellow pigment production

 

bl+

Wild-type

Production of yellow pigment on the body, wings and face.

bl1

Mutant

Elimination of yellow pigment production.

bl2

Mutant

Elimination of yellow pigment production.

blgf

Mutant

Strong concentration of yellow pigment on the face.

blyf2

Mutant

Moderate concentration of yellow pigment on the face.

Table 3 – Symbols and visual effect of the allelomorphs that occupy the "yellow pigment production" locus.

 

          The bl+ allelomorph is dominant over any mutant allelomorph it is paired with.

          The hierarchy among the allelomorphs is: bl+ > blgf > blyf2. I have deliberately left out the bl1 and bl2 allelomorphs. I believe the best classification for these genes is to say they are recessive to bl+, incomplete dominant to the blgf and blyf2 allelomorphs and also incomplete dominant between themselves.

          The best explanation, I've encountered so far, of the biochemistry involving the genes that occupy this locus comes from an article by Peter Bergman of Sydney, Australia titled "gene function in Yellowface Budgerigars".

          The most direct effect of genes is the production of proteins. The wild-type gene, bl+, possesses the instructions to build an active protein that, in turn, conducts the production of yellow pigment on the body, wings and face. The Bl+ gene will always produce a green phenotype, no matter the bird is homozygous or heterozygous for this allele.

          The bl1 mutation and the bl2 mutation produce distinct proteins. These proteins are different from each other and different from the wild-type protein. In both cases, the "mutant" proteins have lost their active properties making them useless for yellow pigment production. Birds homozygous for bl1 like birds homozygous for bl2, can only produce the respective inactive protein. Such birds are visually blue or white.

          Birds carrying both mutant genes (bl1 and bl2) produce three kinds of protein: pure inactive bl1 protein, pure inactive bl2 protein and hybrid bl1-bl2 protein. Somehow, the hybrid protein regains some of its active properties and is capable of yellow pigment production but only on the face of the bird. This type of visual yellowface results from the association of two genes that alone have lost the capacity to produce yellow pigment. bl1 and bl2, both have the same effect, total elimination of yellow pigment production. Only when combined they produce visual yellowfaces.

          An homozygous goldenface bird produces pure "blgf" protein. This protein is very active on the facial area but incapable of yellow pigment production on the body and wings.

          When the blgf allele is combined with the bl1 three kinds of protein are produced: pure active "blgf" protein, pure inactive "bl1" protein and hybrid "blgf- bl1" protein. This hybrid protein is very active and similar in effect to the wild-type protein. The resulting phenotype is a goldenface bird with intense spillage of green over the body, resembling a green bird.

          Similarly, when the blgf allele is combined with the bl2 allele three kinds of protein are produced: pure active "blgf" protein, pure inactive "bl2" protein and hybrid "blgf-bl2" protein. This type of hybrid protein is inactive or very little active. Yellow pigment production comes mainly if not all from the pure "blgf" protein. Such birds produce less yellow pigment them homozygous goldenface birds resulting on a paler shade of yellow.

          Birds homozygous forthe yellowface mutant II gene produce pure "blyf2" protein. This protein, is capable of moderate yellow pigment production on the facial area. The visual appearance is of a yellow paler than the goldenface.

          Birds heterozygous for the blyf2 and blgf alleles produce pure moderately active "blyf2" protein, pure active "blgf" protein and hybrid blyf2-blgf protein. It is reasonable to assume that both types of pure proteins can produce a rich yellow colour on the facial area even if the hybrid protein turns out to be inactive. Such a bird should resemble an homozygous goldenface.

          The combination of the blyf2 and bl1 alleles on an heterozygous bird results on the production of pure active "blyf2" protein, pure inactive "bl1" protein and a very active hybrid "blyf2- bl1" protein. The "blyf2" protein is responsible for the production of yellow pigment over the face but such a bird resembles a green because of the spillage effect caused by the hybrid protein.

Genotype

Effect of the locus that controls yellow pigment production

 

bl+ bl+

Production of yellow pigment on the body, wings and face.

bl+ blgf

bl+ blyf2

bl+ bl1

bl+ bl2

blgf blgf

Strong production of yellow pigment on the face

blgf blyf2

blgf bl1

Strong production of yellow pigment on the face with spillage of yellow pigment over the body

blgf bl2

Strong production of yellow pigment on the face

blyf2 blyf2

Moderate production of yellow pigment on the face

blyf2 bl1

Moderate production of yellow pigment on the face with spillage of yellow pigment into the body

blyf2 bl2

Moderate production of yellow pigment on the face

bl1 bl1

Total elimination of yellow pigment production.

bl1 bl2

Elimination of yellow pigment production from the body and wings (visual yellowface)

bl2 bl2

Total elimination of yellow pigment production.

Table 4 – Visual effect of the pairs of allelomorphs that occupy the "yellow pigment production" locus.

          Till now I have been careful not to say that a bird with normal melanin production is blue or that a bird with yellow pigment production is yellow. In order to truly understand a bird's colour we must analyse both loci simultaneously. If this task seems difficult, one should first try to understand the effect of each locus and then combine both effects. Remember, when normal production of melanin occurs, the body feathers reflect blue light. If yellow pigment is also produced, it works as a filter over the blue radiation and the bird is visually green.

Genotype

Phenotype

Locus for melanin production

Locus for yellow pigment production

 

 

dil+ dil+

bl+ bl+

Normal green

dil+ dilgw

bl+ bl+

dil+ dilcw

bl+ bl+

dil+ dil

bl+ bl+

dilgw dilgw

bl+ bl+

Greywing green

dilgw dil

bl+ bl+

dilgw dilcw

bl+ bl+

Full bodied greywing green

dilcw dilcw

bl+ bl+

Clearwing (or yellow wing) green

dilcw dil

bl+ bl+

dil dil

bl+ bl+

Yellow-green dilute

 

 

 

dil+ dil+

bl+ blgf

Normal green

dil+ dilgw

bl+ blgf

dil+ dilcw

bl+ blgf

dil+ dil

bl+ blgf

dilgw dilgw

bl+ blgf

Greywing green

dilgw dil

bl+ blgf

dilgw dilcw

bl+ blgf

Full bodied greywing green

dilcw dilcw

bl+ blgf

Clearwing (or yellow wing) green

dilcw dil

bl+ blgf

dil dil

bl+ blgf

Yellow-green dilute

 

dil+ dil+

bl+ blyf2

Normal green

dil+ dilgw

bl+ blyf2

dil+ dilcw

bl+ blyf2

dil+ dil

bl+ blyf2

dilgw dilgw

bl+ blyf2

Greywing green

dilgw dil

bl+ blyf2

dilgw dilcw

bl+ blyf2

Full bodied greywing green

dilcw dilcw

bl+ blyf2

Clearwing (or yellow wing) green

dilcw dil

bl+ blyf2

dil dil

bl+ blyf2

Yellow-green dilute

 

dil+ dil+

bl+ bl2

Normal green

dil+ dilgw

bl+ bl2

dil+ dilcw

bl+ bl2

dil+ dil

bl+ bl2

dilgw dilgw

bl+ bl2

Greywing green

dilgw dil

bl+ bl2

dilgw dilcw

bl+ bl2

Full bodied greywing green

dilcw dilcw

bl+ bl2

Clearwing (or yellow wing) green

dilcw dil

bl+ bl2

dil dil

bl+ bl2

Yellow-green dilute

 

dil+ dil+

bl+ bl1

Normal green

dil+ dilgw

bl+ bl1

dil+ dilcw

bl+ bl1

dil+ dil

bl+ bl1

dilgw dilgw

bl+ bl1

Greywing green

dilgw dil

bl+ bl1

dilgw dilcw

bl+ bl1

Full bodied greywing green

dilcw dilcw

bl+ bl1

Clearwing (or yellow wing) green

dilcw dil

bl+ bl1

dil dil

bl+ bl1

Yellow-green dilute

 

 

 

dil+ dil+

blgf blgf

Normal goldenface

dil+ dilgw

blgf blgf

dil+ dilcw

blgf blgf

dil+ dil

blgf blgf

dilgw dilgw

blgf blgf

Greywing goldenface

dilgw dil

blgf blgf

dilgw dilcw

blgf blgf

Full bodied greywing goldenface

dilcw dilcw

blgf blgf

Clearwing (or white wing) goldenface

dilcw dil

blgf blgf

dil dil

blgf blgf

White-blue dilute goldenface

 

 

 

dil+ dil+

blgf blyf2

Normal goldenface

dil+ dilgw

blgf blyf2

dil+ dilcw

blgf blyf2

dil+ dil

blgf blyf2

dilgw dilgw

blgf blyf2

Greywing goldenface

dilgw dil

blgf blyf2

dilgw dilcw

blgf blyf2

Full bodied greywing goldenface

dilcw dilcw

blgf blyf2

Clearwing (or white wing) goldenface

dilcw dil

blgf blyf2

dil dil

blgf blyf2

White-blue dilute goldenface

 

 

 

dil+ dil+

blgf bl2

Normal goldenface*1

dil+ dilgw

blgf bl2

dil+ dilcw

blgf bl2

dil+ dil

blgf bl2

dilgw dilgw

blgf bl2

Greywing goldenface*1

dilgw dil

blgf bl2

dilgw dilcw

blgf bl2

Full bodied greywing goldenface*1

dilcw dilcw

blgf bl2

Clearwing (or white wing) goldenface*1

dilcw dil

blgf bl2

dil dil

blgf bl2

White-blue dilute goldenface*1

dil+ dil+

blgf bl1

Normal goldenface, with green spillage over the body

dil+ dilgw

blgf bl1

dil+ dilcw

blgf bl1

dil+ dil

blgf bl1

dilgw dilgw

blgf bl1

Greywing goldenface, with green spillage over the body

dilgw dil

blgf bl1

dilgw dilcw

blgf bl1

Full bodied greywing goldenface, with green spillage over the body

dilcw dilcw

blgf bl1

Clearwing (or white wing) goldenface, with green spillage over the body

dilcw dil

blgf bl1

dil dil

blgf bl1

White-blue dilute goldenface, with green spillage over the body

 

dil+ dil+

blyf2 blyf2

Normal yellowface

dil+ dilgw

blyf2 blyf2

dil+ dilcw

blyf2 blyf2

dil+ dil

blyf2 blyf2

dilgw dilgw

blyf2 blyf2

Greywing yellowface

dilgw dil

blyf2 blyf2

dilgw dilcw

blyf2 blyf2

Full bodied greywing yellowface

dilcw dilcw

blyf2 blyf2

Clearwing (or white wing) yellowface

dilcw dil

blyf2 blyf2

dil dil

blyf2 blyf2

White-blue dilute yellowface

 

dil+ dil+

blyf2 bl2

 

Normal yellowface*2

dil+ dilgw

blyf2 bl2

dil+ dilcw

blyf2 bl2

dil+ dil

blyf2 bl2

dilgw dilgw

blyf2 bl2

Greywing (blue) yellowface*2

dilgw dil

blyf2 bl2

dilgw dilcw

blyf2 bl2

Full bodied greywing yellowface*2

dilcw dilcw

blyf2 bl2

Clearwing (or white wing) yellowface*2

dilcw dil

blyf2 bl2

dil dil

blyf2 bl2

White-blue dilute yellowface*2

 

dil+ dil+

blyf2 bl1

Normal yellowface with green spillage over the body

dil+ dilgw

blyf2 bl1

dil+ dilcw

blyf2 bl1

dil+ dil

blyf2 bl1

dilgw dilgw

blyf2 bl1

Greywing yellowface, with green spillage over the body

dilgw dil

blyf2 bl1

dilgw dilcw

blyf2 bl1

Full bodied greywing yellowface, with green spillage over the body

dilcw dilcw

blyf2 bl1

Clearwing (or white wing) yellowface, with green spillage over the body

dilcw dil

blyf2 bl1

dil dil

blyf2 bl1

White-blue dilute yellowface, with green spillage over the body

 

dil+ dil+

bl2 bl2

Normal blue

dil+ dilgw

bl2 bl2

dil+ dilcw

bl2 bl2

dil+ dil

bl2 bl2

dilgw dilgw

bl2 bl2

Greywing blue

dilgw dil

bl2 bl2

dilgw dilcw

bl2 bl2

Full bodied greywing blue

dilcw dilcw

bl2 bl2

Clearwing (or white wing) blue

dilcw dil

bl2  bl2

dil dil

bl2 bl2

White-blue dilute

 

dil+ dil+

bl2 bl1

Normal yellowface

dil+ dilgw

bl2 bl1

dil+ dilcw

bl2 bl1

dil+ dil

bl2 bl1

dilgw dilgw

bl2 bl1

Greywing yellowface

dilgw dil

bl2 bl1

dilgw dilcw

bl2 bl1

Full bodied greywing yellowface

dilcw dilcw

bl2 bl1

Clearwing (or white wing) yellowface

dilcw dil

bl2 bl1

dil dil

bl2 bl1

White-blue dilute yellowface

 

dil+ dil+

bl1 bl1

Normal blue

dil+ dilgw

bl1 bl1

dil+ dilcw

bl1 bl1

dil+ dil

bl1 bl1

dilgw dilgw

bl1 bl1

Greywing blue

dilgw dil

bl1 bl1

dilgw dilcw

bl1 bl1

Full bodied greywing blue

dilcw dilcw

bl1 bl1

Clearwing (or white wing) blue

dilcw dil

bl1 bl1

dil dil

bl1 bl1

White-blue dilute

Table 5 – Possible genotypes considering both loci and the respective phenotypes.

*1 – Paler shade of goldenface
*2 – Paler shade of yellowface

          From table 5, we can see the combination between the genes that occupy only two loci, are responsible for creating 150 different genotypes that correspond to 40 different phenotypes.

          As I stated earlier, the expression "the green colour is dominant over the blue colour" is the result of years of confusion about the genetics involved on the origin of budgerigar's colours. The terms dominant and recessive are used only to describe the relations between genes that occupy the same locus. Employing these terms to the visual effects (phenotypes) of genes that occupy two different loci can only serve to confuse and discourage young fanciers with knowledge on biology and genetics. No colour is dominant over another!

          Another common mistake is the belief that there is a gene for the green colour and a gene for the blue colour. "Green gene" and "blue gene" are simplifications one must use carefully. This erroneous concept may have become popular because of the nomenclature and gene symbols used on the book "Genetics for budgerigar breeders". Although the authors understood the effects of each gene they opted to call "green gene" to the wild-type gene that determines the production of yellow pigment, and "blue gene" to the mutation associated to the elimination of yellow pigment. However, we know now that when this "green gene" is associated with the gene for dilute or the "ino" gene (each on their respective loci) the resulting bird is yellow. The same way, if the "blue gene" is associated with the "dilute gene" the bird is white. The specific colour of a budgerigar is the result of the combined effects of two different loci.

0

Este sítio em

Best seen with:



Best seen in:



Sign My Guestbook

Clique aqui para assinar o livro de visitas
Read My Guestbook

Clique aqui para ler o livro de visitas

 

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
Chat | Forum | FAQ's | Downloads | Links | Mailing List

 

E-mail me

Privacy Statement

© 2002 – Humberto Reis

Site made by: Tot@l Net Lda.

Special thanks:
www.bravenet.com