Category Archives: FAQ

FAQ: Combinations of alleles of the same gene

FAQ: Combinations of alleles of the same gene are indicated by writing the mutant names one after the other, for example PastelIno. A capital is used to indicate the start of each mutants name.

But how do we write the name of a combination with epistatic genes?

Well here we have an  easy answer: exactly the same as we write alleles of the same gene! The mutant (gene) names one after the other. Why? It are also two (different) alleles that are creating a (non wild type) phenotype.

FAQ: Genetics behind urucum canaries – Urucum kanaries

Unlike wild and domestic canaries (Serinus canaria), the domestic urucum breed of canaries exhibits bright red bills and legs. To identify the causative locus, scientists resequenced the genome of urucum canaries and performed a range of analyses to search for genotype-to-phenotype associations across the genome. They identified a nonsynonymous mutation in the gene BCO2 (beta-carotene oxygenase 2, also known as BCDO2), an enzyme involved in the cleavage and breakdown of full-length carotenoids into short apocarotenoids. Protein structural models and in vitro functional assays indicate that the urucum mutation abrogates the carotenoid cleavage activity of BCO2. Consistent with the predicted loss of carotenoid cleavage activity, urucum canaries had increased levels of full-length carotenoid pigments in bill tissue and a significant reduction in levels of carotenoid cleavage products (apocarotenoids) in retinal tissue compared to other breeds of canaries. They hypothesize that carotenoid-based bare-part coloration might be readily gained, modified, or lost through simple switches in the enzymatic activity or regulation of BCO2.

In tegenstelling tot wilde en gedomesticeerde kanaries (Serinus canaria), of een van de drie dozijn soorten vinken in het geslacht Serinus, vertoont het binnenlandse urucum-ras van kanaries rode snavels en poten.
Om te begrijpen hoe de poot- en snavelkleur bij vogels evolueert en om het verantwoordelijke locus te identificeren, hebben wetenschappers het genoom van urucumkanaries onderzocht. Als mogelijk oorzaak hebben ze een mutatie in het gen BCO2 (beta-caroteen oxygenase 2, ook bekend als BCDO2) geïdentificeerd. Dit is een enzym dat betrokken is bij de splitsing en afbraak van carotenoïden van volledige lengte tot korte apocarotenoïden. Testen geven aan dat de urucummutatie de carotenoïde splitsingsactiviteit van BCO2 tenietdoet. Consistent met het voorspelde verlies van carotenoïde splijtactiviteit, hadden urucumkanaries verhoogde niveaus van carotenoïde pigmenten. Ze veronderstellen dat carotenoïde-gebaseerde kleuring gemakkelijk kan worden verkregen, gemodificeerd of verloren kan gaan door eenvoudige schakelaars in de enzymatische activiteit of regulatie van BCO2.


Genetic Basis of De Novo Appearance of Carotenoid Ornamentation in Bare-Parts of Canaries
Malgorzata Anna Gazda, Matthew B. Toomey, Pedro M. Araújo, Ricardo J. Lopes, Sandra Afonso, Connie A. Myers, Kyla Serres, Philip D. Kiser, Geoffrey E. Hill, Joseph C. Corbo, Miguel Carneiro

FAQ: Where are we with regards to the opaline mutation in Agapornis eye-ring species?

FAQ: Where are we with regards to the opaline mutation in Agapornis eye-ring species?

FAQ: A number of years ago the first opaline Agapornis fischeri appeared on the scene. This sex-linked mutation probably originated in China. In competitions the BVA Masters provides room for the opaline Agapornis fischeri, but not for opaline in the other eye-ring species. This is in spite of the fact that many breeders are working hard to introduce the opaline mutation into other eye-ring species (Agapornis personatus, Agapornis lilianae, Agapornis nigrigenis). Why is it that there is no room (yet) for these at competitions?

Answer: It’s very simple. Developing a good transmutation transmutation (genetic introgression) takes on average 5 F and 5 R generations, which comes to about 10 years. In the case of mutations on the Z chromosome, including opaline, it can take even longer.

FAQ: Can you see the difference between a dec Blue1Blue2 (turquoise) and a DecIno Blue1Blue2 (turquoise) Agapornis fischeri?

FAQ: Can you see the difference between a dec Blue1Blue2 (turquoise) and a DecIno Blue1Blue2 (turquoise) Agapornis fischeri?

Of course, a dec Blue1Blue2 (turquoise) Agapornis fischeri has a light blue shade on the rump, a DecIno Blue1Blue2 (turquoise) Agapornis fischeri has a white / light yellow rump colour.

See picture: on the left: rump of a DecIno Blue1Blue2 (turquoise) Agapornis fischeri and on the right: rump of a dec Blue1Blue2 (turquoise) Agapornis fischeri

FAQ: what is the difference between psittacofulvins and psittacine?

FAQ: what is the difference between psittacofulvins and psittacine?

tThere is no difference. Psittacofulvins AKA psittacine or parrodienes [1], [2, p. 242] is the class of pigments (red, orange, yellow) that is limited to Psittaciformes (parrots).  In Europe in aviculture they prefer to use the more popular name psittacine (it started with the budgies). In scientific publications it is advised to use psittacofulvins.

[1]          R. Morelli, R. Loscalzo, R. Stradi, A. Bertelli, en M. Falchi, “Evaluation of the antioxidant activity of new carotenoid-like compounds by electron paramagnetic resonance.”, Drugs Exp. Clin. Res., vol. 29, nr. 3, pp. 95–100, 2003.

[2]          D. Van den Abeele, Lovebirds Compendium, 1ste dr. Warffum- The Netherlands: About Pets, 2016.

FAQ: Where to order my books?

FAQ: Where to order my books?

Agaporniden, deel 1 en deel 2 – Dutch (2012 – 2013)

Erfelijkheid bij vogels – Dutch (2014)

Lovebirds compendium – English edition (2016) Hard cover, 768 pages.

Antología del Agapornis de Dirk Van den Abeele -en Castellano – (2018) 768 páginas

Les Inséparables –  genus Agapornis – Édition française – (2018) 768 pages.


FAQ: X and Y or Z and W chromosomes?

FAQ: X and Y or Z and W chromosomes?

In aviculture societies in Europe, the sex-chromosomes in birds was, for long years, referred to as X and Y, just as they do in mammals / humans. That was because, most of the articles / books, those days, used X and Y as sex-determining system in birds.

When I became involved in aviculture in 1993, I explained to judges / breeders that in science they used Z and W instead of X and Y. Trust me, nobody believed me. My first article on that subject was rejected by the editor. “Too scientific” and “not interesting for breeders” was his comments. Another editor replaced in my articles, systematically, before publishing, Z and W with Y and X.

I know it sounds strange now, but you have to watch it in the spirit of the times. Lots of people, really passionate by breeding birds, but their biggest concerns were keeping these birds alive and learn how to breed with them. Mutations were popular, but the inheritance was less important. Most of them were already happy if they understood what sex linked and autosomal was and important: they learned to refer to the sex chromosomes as X and Y, and no one could convince them of anything else (and certainly not a novice breeder like me…). Homines quod volunt credunt. LOL.

Only a few authors used correctly Z and W. But because of the language barrier (there are + 90 different languages in Europe), almost nobody in Europe was aware of it, or ….(in most cases) they considered it as ‘not correct’. They did not realise that the use of ZZ and ZW to refer to the sex chromosomes was definitely not new. In the 1960’s scholars already referred to the sex chromosomes as ZZ for a male and ZW for a female [1]. Unfortunately, these publications were rather rare and unknow in aviculture. At the turn of the 21th century other scholars came up with more evidence for the different origin of sex chromosomes in birds and mammals [2]–[4]. It was clear that the avian sex chromosomes evolved from a different ancestral pair of autosomes than the X and Y chromosomes in mammals. But even then, it was not accepted / important in aviculture.

When I wrote my first book in 2004, I was ‘strongly advised’ to use X and Y (I had to keep things simple, it had to be understandable for the novice breeder etc….). Believe me, I really felt uncomfortable with it, so …. I mentioned in the same chapter, that scientifically it was Z and W [5, p. 101].

In the mean while I was still trying to convince others to refer to sex chromosomes as ZW and not XY. But no luck. That period we were also working on the International naming system, so it was important to do it step by step, because most aviculturists were (are??) very conservative.

More and more scientific publications on the avian sex chromosomes became available [6] and we had extra sources to refer to, but even then, most organizations refused the use of Z and W. So we decided within MUTAVI and Ornitho-Genetics VZW that we waited long enough. I wrote an article on this subject in the BVA magazine and announced that from then on, in BVA International, we should use Z and W to refer to the sex-chromosomes in birds. I can assure you that not everybody was happy with it. ?

Now, almost twelve years later, it is common in Agapornis species to refer to the sex chromosomes as ZZ and ZW, but we have to admit, not everybody is on the same track. We know that it is important to stick to one system and internationally bird sex chromosomes are referred to as ZW and not XY. But believe me, after 25 years in aviculture, I have learnt one thing: …to be patient.

But there is good news: younger breeders become involved in aviculture, they are more educated and open for these changes. We have every confidence in their ability to succeed.

Just my thoughts…

[1] S. W. Soukup, “Sex chromosomes and sex-linked genes. By S. Ohno. Springer-Verlag, Berlin, Heidelberg, New York. 192 pp. 1967”, Teratology, vol. 4, nr. 1, pp. 111–111, feb. 1971.

[2] I. Onsman, “Sex-chromosomes in Birds and Mammals; Differences and Similarities”, 1998. [Online]. Beschikbaar op:

[3] J. A. M. Graves en S. Shetty, “Sex from W to Z: evolution of vertebrate sex chromosomes and sex determining genes”, J. Exp. Zool., vol. 290, nr. 5, pp. 449–462, 2001.

[4] J. A. M. Graves en R. J. W. O’Neill, “Sex chromosome evolution and Haldane’s rule”, J. Hered., vol. 88, nr. 5, p. 358, 1997.

[5] D. Van den Abeele, Lovebirds, owners manual and reference guide, 1ste dr. Over dieren, 2005.

[6] R. Stiglec, T. Ezaz, en J. A. M. Graves, “A new look at the evolution of avian sex chromosomes”, Cytogenet. Genome Res., vol. 117, nr. 1–4, pp. 103–109, 2007.

FAQ: genetic symbols and formulas

FAQ: why are you using different genetic symbols / formulas in your book than in mammals (humans)? Did you invent it?

Answer: No, but I wish I did (LOL). In birds they developed their own genetic system during the years, but it was the English animal geneticist Professor Francis Crew who introduced it in his book: ‘The genetics of budgerigar’ (1935).  He was a pioneer in his field leading to the University of Edinburgh’s place as a world leader in the science of animal genetics.

Later, all other authors also used this system in their books. So, it became in most aviculture clubs the standard. Of course, during the years, the system has been expanded with new symbols and adapted where necessary by several authors. But it is always the same basic. So, it was self-explanatory for me that I used this system in my book.

Crew, F. A. E., & Lamy, R. (1935). The genetics of the budgerigar.

FAQ: is it possible that jade is not a basic mutation but a crossing-over between marbled and cinnamon?

FAQ: is it possible that jade is not a basic mutation but a crossing-over between marbled and cinnamon?

No, it is not. For a start marbled is an autosomal mutation and cinnamon a Sex-Linked mutation. That means that these mutations are on different chromosomes. So a crossing-over between them is not possible.

Other question is if jade is a normal combination of cinnamon and marbled? So a cinnamon marbled green bird?

Again no, we examined the feathers and we are sure it has nothing to do with cinnamon. But if you are still doubting, you can easily test it yourself. If jade is a cinnamon marbled green you can combine a jade (cinnamon marbled) male with a green hen. Then the offspring should be cinnamon green/marbled hens  and green/cinnamon/marbled males. Breeders who have these jades can confirm this is not the case.

So as far as we know, jade is a basic mutation.

FAQ: blue x blue = ??? green??

In 2017 I was contacted by the owners of ‘Aviario Gonzalez Pradas’. They had a pair of two blue Agapornis personatus. In the first nest there were to their surprise three blue and two green chicks. When they announced this on the internet, almost everybody was laughing. For most breeders this is impossible.

And indeed in 99% of all cases the offspring of blue x blue will be blue, but there are some situation where the progeny phenotypes do not match the Mendelian principles. We know now that genetics is a lot more complicated than Mendel’s laws (genes and alleles), some cases of genetic inheritance can be far more complex than simple Mendelian inheritance.

So this is indeed possible. It is rare but it is possible. It is no joke!!

We are working on this, we collected DNA from these birds and we are hoping to get more answers in the future. As soon as we have more info available, you will read it all in the BVA-International magazine.

FAQ: non pied youngsters from dominant pied x dominant pied

FAQ: normal green – non pied – youngsters from a couple dominant pied x dominant pied, is this possible?

Of course it is.

Since a bird has two genes for dominant pied, it can be single factored (SF) dominant pied (only one gene of the pair is mutated) or it can be double factored (both genes of the pair are mutated). If we combine SF dominant pied x SF dominant pied, we have 25% probability of normal – non pied – youngsters. 50% probability of SF dominant pied and 25% probability of DF dominant pied.

Keep in mind that, there is no visual difference in DF or SF dominant pied birds.

FAQ: are combinations of alleles of the same gene on the Z chromosome only males?

FAQ: are combinations of alleles of the same gene on the Z chromosome only males? (PallidIno or PaleIno or PalePallid)

Indeed, since it are both alleles of the same gene, and only a male has two Z chromosomes, it can only be a male. Females only have one Z chromosome. So there are no female PallidIno birds.