Agapornis fischeri dominant reduced (nm) – mutationem novum
Door Dirk Van den Abeele
MUTAVI, Research & Advice Group
Published in BVA-International journal August 2019
In 2008 an “almost completely yellow” Agapornis fischeri was born in the bird room of hobby breeder Harry Bens. At first glance Harry thought he was dealing with a dec green, but on closer inspection the bird looked a bit different. The legs and nails are slightly paler than dec and the rump colour is more present, more blue in colour. The flight feathers are quite varied in colour. There are yellow outer flags, grey edges on some feathers and there are some areas which, just like recessive pied, have a light green wash. The bird came out of the bloodline of which the first misty Agapornis fischeri was produced. [1, p. 536]. The first thing that sprung to mind was, maybe it is a combination of misty and dec?
We all know Harry as a passionate breeder with a lot of experience setting up test matings and with this mutation it was no different. Yet it seemed not as simple as one would think in these early stages. It was quick to see that this mutation has a dominant profile compared to the wild form, but a clear inherittance pattern was not recognisable. Some offspring looked a bit like SF misty, others had an edged-like pattern and some where as good as completely yellow. These birds needed a temporary name and so Harry called them *dominant yellow*.
A year later I saw some yellow birds for the first time with Johan Kip in the Netherlands, which he called the “crazy yellow phenotype”. These are also yellow but appear to look a little more like SF and DF dominant edged birds in terms of phenotype. However, there are differences in the flight feathers and the overall body-colour is also different. In addition, with this mutation the size of the mask is not affected, unlike the DF dominant edged. When it was questioned whether this is the same mutation that Harry has, test matings had to be set up to provide answers. Unfortunately it wasn’t that simple as there were very few young in the earlier years. It was clear that we had to be patient.
What was inevitable also happened, both with the birds of Harry Bens and Johan Kip. Birds (combined and masked by other mutations) ended up in the bird room of other breeders. Others were sold as *dominant yellow* – this of course caused the necessary confusion. Most of them considered these birds to be *dominant yellow*. Some enthusiasts combined both with each other and that gave quite diverse breeding results. Everything was then placed under the label *dominant yellow*. For the majority, the same birds appeared but over time it became clear that it wasn’t quite so.
With the birds that came from the bloodline from Johan Kip we could see a clear sex-linked incomplete dominant inheritance after a few years. With those from Harry Bens the outcome was autosomal dominant. It was now clear that we are dealing with 2 separate mutations. For all certainty, a few test-mating’s were set up from the 2 bloodlines and these ended up confirming the sex-linked incomplete dominant inheritance of the bloodline from Johan Kip.
In Catherina Parakeet [Bolborhynchus lineola] we also have a sex-linked incomplete dominant mutation . At the time it was called SL dominant greywing by Inte Onsman. The question was whether we was dealing with the same mutation in Agapornis fischeri? Although they look very similar, we can conclude this based on appearance alone and feather research needed to be conducted.
Meanwhile, Willie Mathews from South Africa had already informed us that he had a sex-linked incomplete dominant mutation in Agapornis fischeri. According to Willie, it inherited identically to the SL dominant greywing mutation in the Catherina Parakeet. Willie thought he was dealing with *dominant yellow* and let us know that *dominant yellow* definitely inherited SL incomplete dominant . Willie was correct, his observations were correct only it wasn’t the *dominant yellow* birds he had in his collection, it was the SL incomplete dominant greywing. Several enthusiasts in South Africa, Germany, Denmark and the Netherlands confirmed this theory, some used the name greywing, others decided to place them under the denominator ‘SL edged’. It was clear that this had to be approached, we wanted to find the proper answer.
At the beginning of this year it was possible for us to compare both mutants via electron microscope. This showed a similarity between the SL incomplete dominant greywing Agapornis fischeri and the SL incomplete dominant greywing Catherina Parakeet. We have therefore suggested that this mutant in Agapornis fischeri should also be called SL incomplete dominant greywing.
One issue was a wrap, but there was still many unanswered questions regarding the *dominant yellow* Agapornis fischeri. Fortunately there were several enthusiasts who had paired these birds to green wild form for several generations. What happened here is not exactly a common thing. Some chicks looked misty, some looked edged and others were almost completely yellow. We could already exclude sex-linked incomplete dominant inheritance for sure, and autosomal and sex-linked recessive inheritance too. Left then with autosomal dominant.
But with autosomal dominant inheritance we see most mutations have a clear SF and DF phenotypes (autosomal incomplete dominant then), but this has not been the case with the test-pairings.
As with dominant pied we see this mutation has a whole range of colour hues  and there is no eumelanin in certain feather fields, scattered randomly across the body. With these *dominant yellow* birds there seems to be a disturbance in the tyrosinase process, where there are no patches, but rather various degrees of eumelanin reduction. For this reason we propose to call this mutation dominant reduced. In the green series we would talk about dominant reduced green and in the blue series dominant reduced blue.
Genetically, this means that dominant reduced with the diverse carriers for this mutation can exhibit a variable phenotype (appearance). This is called a variable expression of a gene. The eumelanin reduction in theory can vary from 0.1% to almost 100%.
What we have also taken into account with this mutation is that it is possible that the frequency with which the mutation expresses is also incomplete. Then we are speaking of incomplete penetrance of a gene. Simply put, this means that not with all carriers of this mutation (gene), the mutation is manifested. BUT – that still needs further investigation. So all the information regarding breeding outcomes from these birds is still welcomed by us!
It is well proven that this is a new mutation, the key question remains of course whether/how judges will accept this mutation in shows? Given the variable expression of the gene, it is not so easy to determine which form is the most beautiful and most desired during shows. After all, this will determine what type is included in the standard requirements. This is not an easy task when we know all the different phenotypes. Nevertheless, as always I plead for these mutations to be given a chance – where there is a will there’s a way. I wish them all the wisdom with this.
Keep up the good work!!!
 D. Van den Abeele, Lovebirds Compendium, 1ste dr. Warffum- The Netherlands: About Pets, 2016.
 D. Van den Abeele, “Voorlopige conclusie over de nieuwe mutatie bij de catharinaparkiet [Bolborhynchus l. lineola]”. 11-apr-2007.
 “SL dominant greywing mutation in Agapornis fischeri???”, Dirk Van den Abeele, 07-nov-2018. [Online]. Beschikbaar op: https://www.ogvzw.org/?p=14671. [Geraadpleegd: 10-jun-2019].
 I. Onsman, “The Involvement of Recessive Pied in the Origin of the Dark Eyed Clears in the Budgerigar [Melopsittacus undulatus]”, www;mutavi.info, 29-dec-2003. [Online]. Beschikbaar op: http://www.mutavi.info/index.php?art=blackeye. [Geraadpleegd: 10-jun-2019].