It was in 1960 that the first zebrafinch pale Brown back appeared in Belgium.
Let us try to understand how such a combination of colours could have been born.
It is known that the brown and pale back factors, related to sex, are located on X chromosomes, but different and at different locations (loci): (1) and (2).
They are therefore not normally linked (otherwise all the browns would also be pale backs: which is not the case).
How could they get linked on the same chromosome ? (3)
When you mate a brown male with a pale gray back female (or vice versa), each time you get gray males, carriers of brown and pale backs. Each male therefore has two different X chromosomes: One carries the "brown" "no light back" genes, the other carries the "no brown" and "light back" genes. Being recessive, none of these genes can be expressed since they are in a single copy; being non-alleles, neither can dominate the other; It is therefore a natural gray color that is expressed.
How will these genes be transmitted by the male to his offspring ? To understand it, some explanations are necessary.
Chromosomes are very long molecules (2 millionths of a mm thick, average 5 cm long in humans) that are normally entangled with each other in the nucleus of the cell. At the time of meiosis (cell division allowing, in males, the formation of spermatozoa from the mother cells of the testes), these chromosomes split into two rigorously identical chromatids linked together by a centromere.
Each chromatid then spirals. Only then does the chromosome become visible under the optical microscope. The chromosomes group together and join two to two homologous pairs.
During this phase, two chromatids of the two joined chromosomes can cross, break and then join together by exchanging more or less important segments. This is the phenomenon called spanning.
The “brown” gene could thus be found linked to the “pale back” gene on the same X chromosome. A gray male with brown back and pale back can (but only this way) produce pale gray, gray, brown back and pale brown back females. (12.5% of each).
With this crossing over, this same male could also have:
• Crossed with a pale back female: 12.5% of pale gray back males split brown.
• Crossed with a brown female: 12.5% of brown males split pale backs.
By mating one or the other of these with their "pale brown back" sister, it is possible to obtain (in 3rd generation): 25% pale brown back males and 25% pale brown back females.
A : Normal
B : Spirally contracted
C : Schematized
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 colors. 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 centimeters 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 ?
The aim of this article is not to establish an unstoppable rule for the recognition of a gray male split (carrying) the black breast mutation. Rather, it aims to gather the clues that will allow you to identify it.
For this, every detail of the mutation is taken over, according to what I observed during the selection of my strain of gray black chest.
Before starting to analyze each possible clue, it seems important to me to bear in mind that the black chest mutation changes the shape of the drawings. To identify a split of the black chest mutation, I also advise you to take into account all of the clues described in this article.
Let’s proceed and analyze the phenotype of a gray black breast from the head to the rectrices in comparison to a gray split the black breast mutation. To identify each descriptive term used, you can use this diagram : Descriptive terms in zebrafinch .
1. Mustachial line
Black chest : The moustachial line will be pronounced and intense black.
Split (/) Black chest : The moustachial line may be more pronounced than on a gray, however this does not constitute for me a sufficient clue.
2. Tear line
Black chest : The tear line disappears (ideally according to the standard) or only a fine line remains.
Split (/) black chest : Different cases depending on the force of expression of the mutation in the split.
- The tear line is present and fine :
- Tear line is present and wide :
- In some cases, the tear line of a split black chest may also be absent. It will be necessary to rely on the other clues to know if it is a split or a black breast in its own right.
Black chest : The drawing of the cheeks will extend up and back of the head.
I made this glossary to illustrate in photos the existing mutations in the zebrafinch.
He can help you identify the mutation (s) of your zebra finches.
Important precision :To identify the genotype of your zebrafinch, it will be necessary to take into account that a zebra finch can carry a mutation without being mutant.
Being a carrier (/ , split) of a mutation means that it is partially present (genetically speaking). from the visual point of view the partially carried mutation will not be seen or only by some clues present in the appearance of the bird.
In this case, it will be necessary to have a trained eye to determine the genotype. Sometimes check couplings will be necessary.
Your zebra finch can also have several mutations, the possible combinations are numerous.
This glossary is based solely on the phenotype (visual characteristics) and single mutations (not combined).
The gray zebrafinch is not a mutation, it is the original (wild) type.
1. Gender-related mutations
The female can never be a split, so she is either mutant or non-mutant.
The male can be a split of the mutation.