Parblue mutations – PPR partial psittacine reduction

Lots of breeders are asking questions about possible new alleles of the blue locus in ringnecks.
I am afraid that the answer to this question is not that easy. Till now, only 2 “parblue” loci are recognized: aqua and turquoise. That doesn’t mean that other alleles are not possible. The only problem is how to determine that a particular phenotype is indeed a new allele, because a PPR (partial psittacine reduction) mutation is not as simple as we might think.

The blue colors seen in feather barbs of several bird species is produced by interference. But not only this interference has its influence on the final color, lots of other factors can change the visual color of a feather, so also a parblue feather.

Here is list with possible factors that can change the color

Structural changes:

  • The width of the spongy zone (is also related to the dark factor)
  • The nanostructure of the keratin in the spongy zone (is also responsible for the violet factor)

Chemical changes:

  • Of course the amount of psittacine left in the cortex will change the color of a parblue. (Now we consider a parblue with an equal reduction in all feathers (+/-50%) as aqua and the turquoise allele gives us a variable reduction in the feathers.)
  • The chemical composition of the keratin

Genetic causes that can change the color:

  • Combinations with other parblue alleles
  • Combinations with other mutations: slaty, misty, etc
  • Anticipation of the turquoise locus can change the amount of psittacine (a good example is the roseicollis, there the turquoise birds are visually almost completely blue, just by selection on the most ‘blue’ birds)
  • Crossing-overs can combine different factors and give us the wrong impression that we are dealing with only one mutation
  • Pleiotropy, modifying genes and polygeny, translocations etc. All these processes can also influence the color of an existing parblue gene without being a new mutation.

So as you can read, a parblue is not only a matter of more or less psittacine reduction.

I can image that some breeders are waiting for straight answers, but that is for the moment not possible since all these factors can be responsible. We can not determine if a different phenotype is indeed a mutation or a different allele of an existing gene only by examining cross sections of feathers. We need more and liable info on this. So instead of arguing, I suggest that these breeders better start to set up some serious breeding programs.

If there are ‘other par blues’, we have to do lots of test matings. Combinations with pure wild types are strongly recommendable. Only that way we will be able to breed pure homozygous parblues. If we have those homozygous phenotypes we can start to combine them with other proved alleles so we can see what is happening. That will take lots of time, but it is the only way to get some clear answers in the future.
Remember a phenotype is not always a mutation – (genotype) …. just my thoughts .