 | ||
The Slate budgerigar mutation is one of approximately 30 mutations affecting the colour of budgerigars. It is the underlying mutation of the Slate variety.
Contents
Appearance
The name 'Slate' is derived from the appearance of blue-series Slates, particularly the Skyblue Slate, which is close in colour to a Light Grey but with a more bluish tone.
The Light Green Slate is intermediate in shade between a Light Green and a Light Grey-Green. In both blue- and green-series Slates the cheek patch is purplish-grey or deep violet, somewhat like the cheek patches of Mauves. The long tail feathers are a little darker than the corresponding non-Slate. Other features are unaffected by this mutation.
The Dark mutation produces a more noticeable effect in combination with Slate than it does with Grey, but these darker Slate shades differ from one another very much less than Skyblue, Cobalt and Mauve differ. The Cobalt Slate and Mauve Slate are distinctly darker than the Skyblue Slate, with the Mauve Slate being very dark. When Violet is also introduced the resulting Violet Mauve Slate is said to be extremely dark, of a dense blue-black colour.
Genetics
The Slate mutation is sex-linked, the locus of its gene being carried on the X chromosome. It is recessive to wild-type. The gene locus has the symbol sl. The wild-type allele at this locus is notated sl+ and the Slate allele is notated sl.
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 Slate (or any other sex-linked mutation). In cocks, because Slate is recessive, the Slate allele must be present on both X chromosomes (homozygous) to be expressed in the phenotype. Cocks which are heterozygous for Slate are identical to the corresponding Normal. Such birds are said to be split for Slate, usually written '/slate'.
The table on the right shows the appearance of all possible genetic combinations involving just the Slate mutation.
The Slate 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, Ino and Opaline mutations. The cross-over or recombination values between Slate and these linked genes have not all been measured, but the opinion has been expressed that there is a close link between Opaline and Slate. As several Cinnamon Slates were bred without difficulty, it seems likely that the linkage between Cinnamon and Slate is not close. However, these opinions are not borne out by the only measurements to date . In these, Inte Onsman found 22 crossovers between Opaline and Slate in 54 hens bred, which gives a cross-over value of 41±9%, almost no linkage at all. He provides no figures, but suggests the linkage between Cinnamon and Slate is around 5%.