Sometimes it is helpful to use genetic symbols rather than writing the full name of each gene. Using symbols also makes it easier to work out the results of a particular pairing.
There is a general system for deciding the name and symbol for each gene. I will describe it using our trusty Green and Blue genes. One day the gene that causes the wild type color of Green mutated so that it started to make Blue budgies. So how do we name and decide on the symbol for our mutated gene?
Naming - a gene is named after the effects of the mutated gene, so in this case the gene is called 'blue'. (As there are more than one gene that produce a blue effect it is in fact called 'blue1').
Symbol - the symbol for a gene is usually the first one or two letters of the gene name, so in our example the gene is called 'blue1' and its symbol is 'bl1'.
We now have two forms, or alleles, for this gene; the one that makes the budgie green and the one that makes it blue. So how do we differentiate them? We can't write them both as 'bl1'!
As you know a budgie has two copies of each gene. When it has two different alleles of a particular gene they are either dominant or recessive to each other. (For more information on these types of inheritance go back to the Budgie Genetics page.) So the allele that is dominant is written in upper case and the allele that is recessive is written in lower case. In our example that means:
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 alleles for Green
Bl/bl1 = one allele for Green and one for Blue
bl1/bl1 = two alleles for Blue
So now 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.
Heterozygous = two alleles different, so a budgie with Bl/bl1 would be said to be heterozygous, or 'split' for the blue gene (called Green split Blue and written as Green/Blue).
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.
Here is a list of the genetic symbols for the various budgie colours and varieties.
So what can 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!