Genetics and selection criteria
Articles on genetics and on criteria such as type, size, designs, color, etc.
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).
The term English type for some zebrafinch is sometimes used, but what is meant by "English type" !?
Can this type of bird (see video) qualify as an English type ?
Where is it enough that the bird comes from England ? ... Or on the contrary, is it even more typical !?
Young zebrafinch of English type in video :
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.
A : Normal
B : Spirally contracted
C : Schematized
The breeding and competition of zebrafinch has grown considerably over the past fifteen years. In order to improve the size of the new mutations, breeders also have recourse to conventional "split" birds.
Some manage to combine several mutations. All this made it essential to know a minimum of applied genetics. It is this minimum that I would like to present to novice breeders.
This is not a complete course in genetics, but a simple presentation of the method I use preceded by some basics.
2. The zebrafinch and its mutations
A zebrafinch has a number of visible characters (size, shape, designs, color, sex) that constitute its phenotype. It can have, in addition to other unexpressed traits (it is said to be a split). The set of traits, expressed or not, is called the genotype.
A young zebrafinch grows out of an egg cell, the result of the fusion of the nucleus of a father's sperm and the nucleus of the female's egg. The bird's genetic program is already there: A series of cell divisions and coded information will (or not) trigger the appearance of the characters. The encoded information is carried by genes located on long filaments contained in the nucleus: chromosomes.
All chromosomes go in pairs: each chromosome therefore has its counterpart.
There are two categories of chromosomes :
- Sex chromosomes :
• XX in the male
• XY in the female
- Autosome chromosomes.
The gray zebrafinch living in Australia is the source of all of our farmed zebra finches. It has a whole set of genes distributed in its chromosomes.Whenever a new mutation has appeared, there has been a change in an original gene (and it has been shown to be hereditary). The original gene and the mutated gene are located in the same place called a locus on each of the homologous chromosomes.
Both genes are alleles.
A bird is pure (homozygous) when all of its alleles carry identical information.
A bird is heterozygous when at least one pair of alleles carries different information about the same trait.
We currently know about twenty different mutations of the gray zebrafinch.
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 ?
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.