Over the past few years, most Zebra Finch breeders in Australia have come to understand the logic of the Marked White Series of mutations being grouped together. With this article I hope to explain the current knowledge on this group of mutations and what the various forms (Marked White, Chestnut Flanked and Cream Backed) actually are and how other genes modify this group.
     For a long time now, breeders in Europe and elsewhere have recognised that like all colour mutations (except white), Marked White can be combined with other mutations. And although the differences may be slight, variations caused by these combinations can be identified. They have standards for both grey  and fawn forms of these birds. Nowhere else  apart from Australia, are the Marked White and Chestnut Flanked variations separated.
     Put simply, these two classes of birds are but variations of each other at either end of extremes. We have tried to select for either end of the spectrum when setting our two standards. The bird with no marking dilution we have called Marked White and the bird with the markings diluted we called Chestnut Flanked. It is important to know when reading foreign articles that they universally call the mutation Chestnut Flanked, their aim being to have full colour markings, and the dilute birds are viewed as poor quality (nothing more). The difference between our two birds is genetic, but not simply genetics controlled by a single gene that can be seen separately. Instead the difference is caused by modifying genes that can be carried by other mutations without visible effect, yet  interact with the Marked White/Chestnut Flanked gene in a multitude of ways to give all the variations we see.
     Some people have suggested that the Marked White we have today is not the 'pure' form , that somehow it has been changed by other genes . Older fanciers talk about the old days and the Marked Whites with the beautiful black markings, that were lost by inbreeding with Chestnut Flanked. If these statements are true then the original Marked White no longer exists and the standard we have today is for a selected form of Chestnut Flanked. But I can not help having doubts about the accuracy of memory, when the same mutation overseas has the same problems we have - with faded tail bars, faded cheek patches. If the mythical 'perfect' Marked White ever existed, surely the large number of breeders internationally would have saved it or resurrected it if it was possible. Whilst the Marked White and the Chestnut Flanked are but variations, there are distinct genetic combinations of the Marked White/Chestnut Flanked gene with other genes. As mentioned earlier, the fawn gene can be combined with the Marked White/Chestnut Flanked gene. It does however require crossover to combine the genes, a relatively uncommon occurrence in the case of these two genes. Once you have them linked though, it is also difficult to separate them. When the two genes are combined, the result is all 'Black Markings' changing from grey series to fawn series. You can therefore have a Fawn Marked White and a Fawn Chestnut Flanked as well as all the Marked White/Chestnut Flanked variations you know of.
     The Fawn Marked White is what the South Australians had in reasonable numbers and called Chestnut Flanked White. Unfortunately because some societies in the Federation could not understand this issue, and  instead of recognising the bird for what it was, we  had the Fawn Chestnut Flanked standard created. This combination does exist but is not as attractive as the Fawn Marked White. Interestingly, the people instrumental in forcing this standard upon the Federation, are now questioning its existence. Both Fawn Marked White and Fawn Chestnut Flanked are recognisable phenotypes, but I would not push for standards for both as whilst they exist, their popularity is insignificant.
     The Marked White/Chestnut Flanked gene can also be combined with the Dilute Blue/Silver gene. Once again a discernible phenotype occurs. The action of the Dilute Blue/Silver gene is to further dilute all markings and clear out the body. The effect is greatest in the cheek patches where the two genes are able to eliminate all pigment and produce a white cheek patch. I like to call these birds Silver Chestnut Flanked due to the white cheek patches. However quite dark Dilute Blue genes will still create a white cheek patch when combined with the Chestnut Flanked gene.
     Pied, Yellowbill, Blackface and Blackfront can all be combined with the Marked White/Chestnut Flanked gene with the outcome being determined without difficulty.
     Finally we come to the Creamback issue. This bird (for show purposes) is a modification of a variation and a combination. The first modification is the Creamback gene that creates a creamy back on any other of the Marked White/Chestnut Flanked variations. It does not exist by itself, but it can be expressed on anything in the Marked White/Chestnut Flanked series including the fawn combinations. The Creamback modifier is dominant to white back. The Creamback for show standard is the Cream Backed modification of the Fawn Chestnut Flanked. This bird can also be combined with the Dilute Blue gene to produce the Silver Creamback - a Creamback bird with white cheek patches.
     How many of these birds should be recognised? All should, but not all or even many should have standards. Every judge must recognise and understand how these combinations and variants form so they can classify and assess the birds they are asked to assess. But it is pointless having standards for every bird possible if no one is interested in showing them.
     It is also important that standards be distinct from one another. So with this in mind I am happy with the status quo for a number of mutations, but would like to see the fawn series Chestnut Flanked become a Fawn Series Marked White (this is after all what it was supposed to be). At present we have three variations of the Chestnut Flanked form but only one of the Marked White form. It would be a lot easier to separate them if we had two for each.