If you ask at a meeting of zebrafinch lovers questions about the genealogy of the masked, pastel, or black cheeks, we are certain to receive the correct 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 intermediate, others dominant, etc.
Nevertheless these characteristics follow the laws of Mendel. Many breeders do not believe this explanation, but it is true. It seems that laws no longer behave strictly as in other color mutations. A wider variation in format (size), shape of the head, etc ... seems normal.
In nature, we find in zebrafinch the same variation in the format. And, in the process of domestication, this difference in variation has increased. Our cultivated zebrafinch are on average two centimeters wider than their ancestors in the wild.
In articles, one always recommends a hard selection at the level of the format and the model taking into account the differences between the parts like the head, the body, etc.
But the format and the model are directed by the genealogy. The body shapes are driven by factors.
The question is: Is there a relationship between the different factors that governs the format, the model, the shape of the head and the beak ?
In my opinion, these factors are independent of each other. Lesser quantities of zebrafinch are found in the correct size and type of beaks, and there are no good-sized zebrafinch; the right kind of beak alone, etc. This is not an advantage in breeding a good size and hard selection is the only way to improve these characteristics.