Simply select the head, chest, and body colours of your desired Gouldian phenotype using the three drop-down menues above, and then press the search button. After a few seconds (sometimes the search takes much more time though) a list of cock-and-hen pairs that can produce your desired phenotype with the highest probability will be displayed. If you have any of these cock-and-hen pairs in your collection you will be able to produce your desired Gouldian phenotype. If you don't, then at least you know which cock or hen to beg/borrow/steal to produce it.
The fine detail
There can be literally hundreds of different cock-and-hen pair phenotypes that can produce a given offspring phenotype. This reverse genetics forecaster will list only those cock-and-hen pairs with the highest probability of producing your desired phenotype.
The probability of producing any given offspring phenotype is shown in the right-most column of the search results table. Just like the gender of any animal, there is no guarantee that you will produce your desired Gouldian phenotype in any given clutch. I.e., even though gender probability is roughly 50%, that does not mean there will be two hens and two cocks in a clutch of four chicks; they may be all hens or all cocks. This is a probability after all.
The database is huge, with over 2 million hen-and-cock phenotype combinations. A search on such a large database takes time, and further time is taken uploading the results and phenotype images to your computer. I'm seeing searches completed within about 10seconds, but your mileage may vary.
The body colour selection menu allows for very fine selection of the silver and yellow shades that are seen in Gouldians. Some of these body colours are only seen with certain chest colours, so please ensure that your selected chest colour is compatible with your selected body colour. For example, if you want a Single-Factor Yellow (male) Gouldian, you must select Purple in the chest colour drop-down menu. If you do choose an incompatible combination of chest and body colour, the displayed phenotype icon (to the right of the menues) will display a large cross through it.
If you notice any errors in the results, please don't hesitate to contact me.
I would like to thank the (forward) Genetics Forecaster of Marek Buransky for providing the inspiration for completing this reverse forecaster. It took quite a while, but after a lot of study of Marek's forecaster I was finally able to understand (to a large degree at least) the "mechanics" of Gouldian phenotype genetics.