Genetic transmission of physical characteristics
If you ask at a meeting of zebrafinch lovers a question about the genealogy of the masked, the pastel, or a black cheek, you are sure to receive the right answer.
But if we ask the genealogy question about the format (size), the shape of the head or the length of the beak, the answers will be multiple and different.
Some will say intermediaries, others dominant, etc.
Nevertheless, these characteristics follow Laws of Mendel. Many breeders do not believe this explanation, but it is true. It seems that the laws no longer behave in a strict way as for the mutations of colours. A wider variation in the format (size), shape of the head, etc... seems normal.
In nature, zebrafinch have the same variation in size. And, in the process of domestication, this difference in variation has increased. Our cultivated zebrafinch are on average two centimetres wider than their ancestors in nature.
In the articles, we always recommend a hard selection at the level of format and model taking into account the differences between the parts such as the head, the body, etc.
But the format and the model are driven by genealogy. The body shapes are driven by factors.
The question that arises is: Is there a relationship between the different factors that govern the format, the model, the shape of the head and the beak ?
In my opinion, these factors are independent of each other. We find, in smaller quantities, zebrafinch in the right size and type of beak, that we do not find zebrafinch in the right size alone; to the right type of beak alone, etc. This is not an advantage in rearing a good size and hard selection is the only way to improve these characteristics.
On the other hand, we know that factors can influence the results of others: They can modify the result, strengthen the result or decrease the result.
We are aware that several factors must work together to obtain a good format. Factors help to manifest together. They’re called polymer factors. These factors drive format and size.
Hans Kloren’s explanation, in his book: "The mating of a strong Mandarin diamond to a small Mandarin diamond, gives us intermediate-sized youngsters. If we breed these young, we would expect the following results: A quarter shows the strong size of the first parent, a quarter shows the small size and the rest looks like young F1. That’s not true. It’s even exceptional if some of the F2 kids look like the strong parent."
What is the explanation ?
Suppose that the strong parent has at the format 4 pairs of factors that are different from that of the small parent. The 4 factors bring a part of the format. The young zebrafinch must have a large format. The first generation of youth (F1) will have the intermediate format because these youths receive from both parents a factor from each pair. According to Mendel’s laws, the next generation (F2) will show all possible combinations of factors, which is actually the case.
In the F2 generation there are few copies that have, of the four factors, the one that offers the possibility of having a good format. The calculation of the odds is similar to the calculation of the "colour" factors. Starting from 4 factors, the possibilities of combination are enormous. The chance of finding the 4 factors together is one in 256. If the format is driven by more than 4 factors, the chance decreases exponentially. The reasoning for the model, the type of beak, etc. is the same.
The fact that most fans are convinced that the format inherits in an intermediate way, is based on the fact that the format of the F1 generation stands in the middle of the parent formats. Intermediary means between the two. It is true to say that the format does not inherit from the intermediary, but that the format of the F1 generation is intermediate.
Hans Kloren assumes that the factors responsible for format and model are recessive factors. In many cases, this is true. But it’s not true for all strains. Some strains give completely different results. Those who bought zebrafinch from Dick Offerman obtained other results by entering these zebrafinch into their stock. The format and model of this strain were dominant and gave F1 and F2 generations of zebrafinch similar to the original zebrafinch.
An example: Luk P. bought two subjects with thin heads in order to manage a strain of symmetrical varietals. He never knew how to remove this fine head from his stump: This shape was dominant.
In most zebrafinch, the format and model are composed by recessive polymer factors, but in some strains there are similar factors (composing the format, the model) playing a dominant role.
Jan Van Looy
Article written in 2007.