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Pastelface Cockatiels
The Pastelface Cockatiel gene is a member of the 'Blue' family of genes or better known as the Whiteface family in cockatiels. It is known in the bird world as the Parblue mutation. It effects the production of the yellow family of pigments as does the Whiteface gene but has only a partial effect hence the name 'parblue'. Some yellow pigment is still present but a more diluted version. This gives us a stunning bird with paler more peachy coloured cheek patches and a lemon colour instead of yellow. It combines beautifully with any of the mutations that alter the structural colour or grey family pigments.eg. cinnamon, pastelsilver. Personally I find it produces some wonderful coloured birds when combined with any other mutation at all as does the Whiteface gene. By altering the colour of the yellow family pigments and not affecting the grey ones some gorgeous contrasts can be seen when the Pastelface is combined with even normal grey pigment.
HeredityThe Pastelface cockatiels gene is autosomal recessive in inheritance. This means that a bird must carry two genes to be visually any autosomal recessive mutation. This is only partly true in the case of the Pastelface cockatiels gene. As I said earlier it belongs to the same family of genes as the Whiteface mutation and thus it is a variation of the same pre-existing gene as the Whiteface. When we have a few different mutations all derived from the same original gene they all occupy the same location on a chromosome. Each bird contains many matching pairs of chromosomes and a gene can only occupy one particular position on any one pair. Within that matching pair of chromosomes there is a one location on each chromosome that this gene can reside. Even though this location is basically reserved for the Whiteface family of genes that doesn't mean they can all be present at the one location at the same time. Only one gene can be in any one location in any bird. It is what is on the second chromosome of a matching pair that will dictate whether the gene can express itself or not. With the Whiteface or 'Blue' family of genes in cockatiels there are 3 possible genes that can occupy this position. They are the Whiteface gene, the Pastelface, or the original wild-type normal grey gene.
When we have other autosomal recessive mutations that consist of only the normal wild-type gene and only one mutant gene eg. pied, the wild-type gene is dominant. So if we have a pied on one chromosome and a wild-type gene on its matching paired chromosome then the wild-type gene will be dominant and prevent the pied from expressing itself. When there is a matching pied gene on both chromosomes then there is no wild-type gene to be dominant and hence the pied is visual. Within the Whiteface family of genes this is only partially the case. Because there are three genes in the Whiteface family in cockatiels any one of these could occupy the particular location in any bird. Likewise any one of these three could be in the position on the matching paired chromosome. This is where the expected results from combinations between these genes differ to the normal autosomal recessive mutation. We know that the wild-type gene is dominant over any mutant gene in normal circumstances. The same applies here. If either the Pastelface of Whiteface gene appear on one chromosome and the wild-type gene on the other then the bird will be visually normal grey. It will be said to be split to either of these two genes. Keep in mind here I am only considering the effect of the Whiteface family and ignoring the presence of any other family of genes. Other families have no effect on the outcome of the whiteface family mutations. The normal rule applies to combinations where there are two whiteface genes or two pastelface genes present. In both cases that gene will be able to express itself and the bird will be visually whiteface or pastelface.
Things change however when we have a pastelface gene present on one chromosome and a whiteface gene on the other. The Whiteface gene is still recessive unless it has a whiteface gene occupying the space on its matching chromosome. Because there is a pastelface gene there instead the whiteface cannot express itself. However it differs with the pastelface gene. It is capable of expressing itself if the whiteface gene is present as its partner on the matching chromosome. It is said to be dominant over the whiteface gene. Two pastelface genes will give a visually pastelface chick as will the combination of one whiteface and one pastelface. The reason for this is that the position of the whiteface family genes is the site where the regulation of psittacin or yellow family pigments production is carried out. When two whiteface genes are present they effectively prohibit all production of yellow family pigments. The Pastelface or parblue gene allows partial production of psittacin so if two pastelface genes are present then the bird will have partial but not all of the normal level of psittacin produced. When the whiteface and pastelface gene are both present together, not all psittacin production is prevented because the pastelface is incapable of totally inhibiting it, thus allowing some pigment to produced. Because of this it is possible for a visual pastelface to be split for whiteface but a visual whiteface cannot be split to pastelface or it would not be visual whiteface. Remember a visual whiteface must have two whiteface genes and they can only be present at one particular location. If a pastelface gene is present on the matching chromosome then there is no space for a whiteface gene and hence it cannot be visually whiteface.
Most visual Pastelface cockatiels in Australia are genetically whiteface/pastelface combinations. They are usually written as Pastelface split to Whiteface to differentiate them from a visual bird that has two pastelface genes. We cannot say the bird is split to both pastelface and whiteface as this would infer it was visually normal grey. As this is not so the above terminology is more correct. When breeding these birds.....and here I refer to the pastelface/whiteface combination.....it is more common and desirable to pair them with a visual whiteface bird. This combination will give both visual whiteface chicks and visual pastelface chicks. There is still some doubt as to the size and vigour bird that has two pastelface genes so by keeping the whiteface present it guarantees quality in our Australian Pastelface Cockatiels.
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