Sometimes it is helpful to use genetic symbols rather than writing the full name of each gene. There is an international agreement on how names and symbols are used as the same genes and mutations are present in many parakeet species. It makes sense to follow a system so everyone is using the same name for the same gene, however, budgerigar clubs tend to stick to what their members are used to instead. I will use the internationally agreed system where ever possible.
So, one day the gene responsible the wild type green colour mutated so that it started to make blue budgies. How do we name and decide on the symbol for our new mutated gene?
Naming - a gene is named after the effects of the mutated gene, so in this case the gene is know called blue. (As there are two genes that produce the blue phenotype in budgies, it is in fact called blue1).
Symbol - the symbol for a gene is usually the first two or three letters of the gene name, in this case: bl, and the original wild type version of a gene is also given a +. In our example the wild type allele is bl+ and the allele which produces a blue bird is bl1. We can now easily distinguish which allele of the blue gene we are talking about.
When a gene mutates the new allele is usually either dominant or recessive to the original wild type. (For more information on these types of inheritance go back
to the Budgie Genetics
page.) So an allele that is dominant to wild type is written in upper case and the
allele that is recessive is written in lower case. In our example bl1 is recessive to the wild type of green so this genes symbol is always written in lower case. So here we have them:
green = bl+
blue = bl1
As a budgie has two copies of each gene there are three possible combinations of the above genes that any budgie can have.
bl+bl+ = two genes for green colour
bl+/bl1 = one gene for green and one for blue
bl1/bl1 = two genes for blue
Next we need terms to describe a bird with two alleles the same (like bl+/bl+ or bl1/bl1) or two that are different (like bl+/bl1):
Homozygous = two alleles the same, so a budgie with bl+/bl+ would be said to be homozygous for the wild type blue gene.
Heterozygous = two alleles different, so a budgie with bl+/bl1 would be said to be heterozygous, or 'split' for the mutated blue gene (called green split blue and written as green/blue).
Finally there are two more useful terms that you are bound to come across:
Phenotype = what your budgie looks like, a description of its physical appearance.
Genotype = what genes your budgie has, a list of the genes that produce the budgies phenotype.
As already mentioned many of the genes present in budgies are also present in other parakeets. Generally the same name is used when the same mutation occurs in different species, so there are a number of species that have the par blue mutation. However, for some reason (probably because budgies are very popular and the clubs large enough to be separate from other clubs) budgie breeders named some of the mutations differently and do not want to change to conform. For example we tend to call the par blue varieties in budgies yellow face blue. It makes sense to adopt the same naming system as used in other species, but I'm not sure that will happen.
There is a list of the genetic symbols for the various budgie colours and varieties that I prefer. It tends towards the internationally agreed symbols, but you may find other lists that use different ones also. This list can be found on the MUTAVI website.
So what do we do with these genetic symbols? We go back to the Budgie Genetics and learn about the different types of inheritance. Then we use the symbols to work out the results of different pairings.... which is lots of fun!