A little history
As we know today, Gregor Mendel, best known for his experiments with peas, was the basis of genetics. He demonstrated through his experiments that if he crossed two peas (F1) with different characteristics such as flower color, leaf size ... Then the offspring (F2) kept the characteristics of a single parent. All the flowers of these young peas had the same color and size of leaves.
It’s as if they “lost” one of the properties. When he crossed these young F2 peas with each other, the F1 characteristics reappeared among the offspring of the F3 generation. Mendel called these characteristics shown by F2: Dominant. And the characteristics hidden in the F2 have been called recessive.
Currently we still call it dominant and recessive. However we do know that Mendel discovered "complete dominance". There are indeed other forms of dominance. We already know these forms so we will mainly bring a few provisions to remember.
We know that genes carry characteristics and that these genes are located on chromosomes. There are genes that deal with the color of the eyes, the color of the legs, the size of the beak… Chromosomes are found in the cells of the body: They are stored in the nucleus of each cell. In each nucleus of each cell are the genes for the color of the eyes, the color of the legs, the size of the beak ... However, the functioning of the “color of the eyes” genes is manifested only in the eyes. In the paws, the "eye color" genes do not show up. Each cell therefore “knows” where it is located in the body and which genes it must activate.
Chromosomes go in pairs, all genes are found in pairs. So for the eye color gene, we have two genes. This also applies to the color of the legs, the size of the beak ... These two genes for the color of the eyes can cause a color of the eyes blue. It is also possible that one gene is responsible for the color blue and the other for the color brown. (which does not mean that the being will have one blue eye and the other brown, the brown of the eyes is dominant over the blue, so both eyes will be brown).
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 ?