genotype

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.

Some concepts

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).

Why are the mutations in zebrafinch of pale back, masked (new type) and masked old type combined with each other so difficult to predict !?
Quite simply because we cannot speak at the genetic level of different mutations but rather of allelic versions of a single gene. The pale back, the masked and the old type mask are due to the same gene but which has three allelic versions.
To understand well let's make the parallel with man, the color of the eyes for example, whatever our eye color, our iris color and coded by the same gene, but this gene has many different versions (alleles) which allow us to have the color panel that we know.

Now that we know a little more about what complicates these crosses, let's take a look at how each allele behaves in relation to each other.
Everything is a story of dominance and co-dominance or recessivity.

A small table to illustrate all this :

*OT = Old type

In this double entry table you can see that it allele dominates the other, the bird will therefore have the phenotype of the allele which dominates, be careful, it is not because the allele is dominated that it does not not influence. See pale back / OT mask, the back is more diluted because of the masked OT allele.

From this result we can draw the first conclusions :

• The pale back can be masked or OT masked.
• The masked can be a masked OT split but cannot be a pale back wearer (pb dominates masked = pb / masked). *pb = pale back
• The masked OT cannot carry a pale back, nor a masked person because the latter two dominate him.

Small practical software allowing to have the probabilities of the results of a mating according to the mutation (s) of the respective parents. It can be put on USB sticks, no need for an internet connection to use it.

Before that, we will obviously need to know the genotype of each parent. To help you determine the mutation or combination of mutations to which your zebrafinch belong, you can refer to: Illustrated glossary of mutations in zebrafinch.
That said, I would say that this application is only an aid. The best thing will always be to understand how each mutation is transmitted. For this, I also advise you to have a good basis to consult the article: Zebrafinch genetics : Instructions.

Here is a site, also available in application, dedicated to the calculation of the genetics of zebrafinch. ZebraCalc allows you to have the probabilities of results depending on the mutations of the respective parents.

Before that, we will obviously need to know the genotype of each parent. To help you determine the mutation or combination of mutations to which your zebrafinch belong, you can refer to: Illustrated glossary of mutations in zebrafinch.
That said, I would say that this application is only an aid. The best thing will always be to understand how each mutation is transmitted. For this, I also advise you to have a good basis to consult the article: Zebrafinch genetics : Instructions.

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 grey back female (or vice versa), each time you get grey 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 grey colour 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 grey male with brown back and pale back can (but only this way) produce pale grey, grey, 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 grey 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.



CHROMATID

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 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 ?

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 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.

3. Cheeks

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).

Grey (GR)

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.

Brown (Br)

1. Define your objectives

First, in my opinion, it is necessary to target and define its objectives: Choice of mutation (s) to be selected, studies of the characteristics of the chosen mutation (s), knowledge of the type of genetic transmission, creating a network of breeder likely to work on similar objectives to have starting subjects. The breeders will need to have confidence in your project and your insight. They will also be concerned about the fate of their surrendered birds.
Essential conditions to then start the construction of a strain and start a selection in order to tend towards your defined objectives like any project.

Finally, define your idea of the bird you want to get. Without forgetting the characteristics of the mutation or combination in which you are projecting yourself.

2. Tips for getting started

Choose the starting zebrafinch with the fewest possible flaws. Be especially careful not to start with birds of uncertain genotype.
Example: If you have a project to build a strain of gray, check if they would not carry a mutation with recessive inheritance (like black chest, black cheeks).

Ask the breeder giving you your first specimens, ask to see the parents to be better fixed. Observe the different qualities and areas for improvement of each one, keeping in mind the zebra finch you want to achieve.
Observe the harmony and the whole of the birds of the breeder, a homogeneity will make you appear a good work of the breeder.

3. What is a strain

You have to imagine the stump of a tree, its trunk and its branches, made up of ancestors, descendants, sisters, brothers, etc. Different methods exist depending on the type of genetic inheritance of the mutation or high combination to advance a strain.