Genetics and selection criteria
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.
A little history
As we know today, Gregor Mendel, best known for his pea experiments, has been at the root of genetics. He has shown by his experiments that if he crossed two peas (F1) with different characteristics such as the color of the flower, the size of the leaves ... Then the resulting (F2) kept the characteristics of only one parent. All the flowers of these young peas had the same color and size of leaves.
It's as if they had "lost" one of the properties. When he crossed these F2 peas between them, the F1 characteristics reappeared among the F3 generation. Mendel called these features shown by the F2 : Dominant. And the hidden features in F2 have been called recessive.
Currently we still call it dominant and recessive. However, we know that Mendel discovered "complete dominance". There are indeed other forms of dominance. We already know these forms so we will especially bring some provisions to remember.
We know that genes carry characteristics and that these genes are located on chromosomes. There are genes dealing with the color of the eyes, the color of the legs, the size of the bill ... The chromosomes are located 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 paws, the size of the beak ... However, the functioning of the genes "eye color" is manifested only in the eyes. In the legs, the genes "eye color" do not appear. Each cell "knows" where it is in the body and what genes it needs to activate.
The chromosomes go by pair, all the genes are found in pairs. For the eye color gene, we have two genes. This also applies to the color of the legs, the size of the bill ... These two genes for the color of the eyes can cause a color of the blue eyes. It is also possible for one gene to take care of the blue color and the other for a brown color. (This does not mean that the being will have one blue eye and the other brown, the brown eye is dominant on the blue, so both eyes will be brown).
Explanations and couplings
Why, these three mutations combined are so difficult to predict ?
Simply because we can not speak at the genetic level of different mutations but rather allelic versions of a single gene. The pale back, the masked and the old type mask (OT) are due to the same gene but which has three allelic versions. You can find the phenotype of each one in photo in this article : Illustrated glossary of mutations in zebrafinch.
In order to understand well, let us make the parallel with the man, the color of the eyes for example, whatever the color of our eyes, our color of the iris and coded by the same gene, but this discomfort has many different versions (alleles) that allow us to have the color panel that we know.
Now that we know a little more, let's see how each allele behaves in relation to each other.
A small table to illustrate all this :
Allèle \ allèle Back pâle Masked Masked OT* Back pâle X Dos pâle Back pâle Masked Back pâle X Masked Masked OT* Back pâle Masked X
* OT = old type
In this double-entry chart you can see that it allele dominates the other, so the bird will have the phenotype of the allele that dominates. Be careful, it's not because the allele is dominated that it does not influence. See also the 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 may be masked or mask OT.
- The masked can be masked OT but can not be bearer of pale back (pale back dominates the masked).
- The masked OT can not be bearer of pale back, nor masked because these last two dominate it.
Female masked gray old type
To know :
- Each bird has two chromosomes so it has twice the same gene (but not necessarily the same allele).
- The pale back, the masked and the masked OT are mutations linked to the sex, they are thus carried by the sex chromosomes. In birds, the male has twice the same sex chromosome (ZZ) and the female has two different sex chromosomes, one of which bears the genes linked to the phenotype (ZW, the W carries the genes related to the phenotype).
Now let's detail each possible coupling. Let's start with the pale back and the masked below.
Male pale back X masked female
Female\Male ZBp* ZBp ZM ZBpZM* ZBpZM W ZBpW ZBpW
*Bp = Back pâle; *M = masked
The raising and presentation of zebra finch has grown considerably over the past fifteen years. To improve the size of the new mutations, breeders have also resorted to the classic "carrier" birds.
Some manage to combine several mutations. All this made it essential to know a minimum of applied genetics. This is the minimum that I would like to introduce to new breeders.
It is not a complete course of genetics, but the simple presentation of the method I use preceded by some basic concepts.
2. The zebra finch and its mutations
A zebra finch has a number of visible characters (size, shape, pattern, color, sex) that make up its phenotype. It may have, in addition to other characters not expressed (it is said that it is a carrier). The whole of the characters, expressed or not, is called the genotype.
A young zebra finch comes from an egg cell, the result of the fusion of the nucleus of a spermatozoon of the father and the nucleus of the ovum of the female. The genetic program of the bird is already there: A sequence of cell divisions and coded information will trigger (or not) the appearance of the characters. The coded information is carried by genes located on long filaments contained in the nucleus: Chromosomes.
All chromosomes go in pairs: each chromosome has its counterpart.
There are two categories of chromosomes :
- The sex chromosomes:
• XX in the male
• XY in the female
- The chromosomes autosomes.
The gray zebra finch living in Australia is the origin of all our zebra-reared finch. It has a whole set of genes distributed in its chromosomes.
Whenever a new mutation has appeared, it is because there has been a modification of a gene of origin (and that it has proved to be hereditary). The gene of origin and the mutated gene are located at the same location called locus on each of the homologous chromosomes.
Both genes are alleles.
A bird is pure (homozygous) when all its alleles carry identical information.
A bird is heterozygous when at least one pair of alleles carries different information about the same trait.
There are currently about twenty different mutations of gray zebra finch.
We distinguish :
a) The dominant mutations
Pastel, crested, cheeks (gray, brown), black face (black-face), cheeks clear.
A mutation is dominant when it is expressed while the mutated gene exists in only one copy. This gene is located on an autosome chromosome.
There are therefore no zebra finch carrying these mutations.
Note: When the two homologous chromosomes each carry a dominant gene, the young is not viable. This is called a lethal factor.
b) Recessive mutations
White, variegated, saddled, white breast, black breast, orange breast, black cheeks, isabelle, agate, yellow beak, eumo.
A mutation is recessive when it is expressed only if the two autosome chromosomes each have the mutated gene.
If there is only one mutated gene, the character is not expressed. The bird is simply "carrier" of the mutation.
c) Gender mutations
Brown, pale back, masked old type, masked new type.
A mutation is linked to sex when the genes responsible for this mutation are located on the X chromosome (s) of the bird (the Y chromosome of the female being empty of genes).
The mutation is expressed in females since they receive from their father the mutated X chromosome. For it to be expressed in males, the mutated gene must be carried by each of the two X chromosomes. Otherwise, the male is only the carrier of the mutation; however, he can pass it on to half of his daughters.
Notes: The "Light Back" and "Masked" genes are alleles of the same non-mutated gene. A Gray male may carry Pale Back and Masked.
A pale-backed male can be a masked bearer, but not the other way around. In this case, even in a single copy, it is he who expresses himself.
The same factor (Pale Back) can be recessive compared to Gray, but dominant over Masked.
The gene "Brown" also located on an X chromosome does not have the same locus as the previous genes.
Anterior to the other two, it is on a different chromosome.
For these genes to be linked (Pale Brown Back, Brown Masked), it took the appearance of a phenomenon that is the subject of another article: Crossing-over.
d) Combined mutations
Many mutations as well as gray can be combined with each other. One can theoretically associate a lot but in practice, it is better to remain cautious: In addition to the many necessary crossings, it is necessary that the bird obtained remains typed and corresponds to the criteria of the standards.
The most famous are :
• Brown pastel
• Gray or Brown cheeks
• Isabelle Black Chest
Black Brown Black Breast or Brown White Brown Pastel combine, for example, a sex-linked mutation, a dominant free mutation and a free recessive mutation.
It is therefore necessary to know how to choose the best crossings to achieve this.
3. Crossing technique
a) Assign each mutation a symbol
We begin by assigning each mutation a symbol: By analogy with the atomic symbols, we can choose one or two letters of the name of the mutation.
The dominant mutations are in upper case, the others in lower case.
Personally, I use the following symbols (From French abbreviations of mutations) :
Fn: Black face
bj: Yellow beak
po: Orange Breast
pb: white chest
pn: black breast
J: Cheeks (Gray or Brown)
jn: Black cheeks
dp: Pale Back
ma: Masked Old type
mn: Hidden new type
Scientists have a + sign followed by the symbol of the unmutated gene.
Example: H (Huppe); H + (not Crested); pb (White breast); pb + (no white breast).
Personally, I find it more logical to write: H + (Huppé); H- (not Crested); pb + (White breast); pb- (no white breast).
In the end, the results will be the same.
b) Write the genetic formula of each bird
On either side of a fraction bar, symbols of the genes carried by each homologous chromosome are transferred, starting with the sex chromosomes.
c) Sex chromosomes
Gray male: XN / XN; Gray female XN / Y
In this case, N means Normal
d) Gender mutation
Brown male: Xbr + / Xbr +; Brown female: Xbr + / Y
Same formulas with dp +, my +, mn +.
e) dominant free mutation
Male pastel gray: XN / XN PL + / pl-; Gray pastel female: XN / Y pl- / PL +
Same formulas with H +, BF +, J +.
Non-mutated recessive factors are written in lower case.
f) Free recessive mutation
Black-chest male XN / XN pn + / pn +; Black breasted gray female XN / Y pn + / pn +
Same formulas with pb +, po +, jn +, pa +, se +, is +, and so on.
g) Combined mutations
Brown male black face black cheeks: XN br + / XN br + Fn + / fn- jn + / jn +
Male pastel pale yellow pastel: XN dp + / XN dp + Pl + / pl- bj + / bj +
Gray male / (/ means carrier) Pale back: XN dp + / XN dp-
Female Brown / Black cheeks: XN br + / Y jn + / jn-
Gray female black face / black breast: XN / Y Fn + / fn- pn + / pn-
Gray male black face / black breast: XN / Y Fn + / fn- pn + / pn-
Male pale back gray / Masked NT (new type): Xdp + / Xmn +. In this case, one could write DP +, since the Pale Back dominates its allele, the NT Mask.
4. Place these formulas in a cross table
We must first remember:
• That each parent transmits to his or her young only one of the two chromosomes of each pair.
• That the grouping in each gamete (spermatozoon or ovum) of these chromosomes is by chance: it is the genetic mixing.
The more the parent has mutated genes on different chromosomes, the more combinations will be possible. This is the only difficulty in this method, but it is inevitable.
Let's start with a simple crossover :
a) Brown male: (XN br + / XN br +) X Female gray XN br- / Y
XN br+ XN br+ XN br- XN br+/XN br- XN br+/XN br- Y XN br+/Y XN br+/Y
Each chromosome of the male (in this case, the sex chromosomes) finds its homologous chromosome provided by the female. It only remains to translate each formula.
Results : XN br + / XN br- Male gray / brown (50%); XN br + / Y Brown female (50%)
b) Male gray / brown: (XN br + / XN br-) X Brown female: XNbr + / Y
XN br+ XN br- XN br+ XN br+/XN br+ XN br-/XN br+ Y XN br+/Y XN br+/Y
Results : XN br + / XN br + Brown male (25%); XN br- / XN br + (25%); XN br + / Y Brown female (25%); XN br- / Y Gray female (25%).
Once the method is acquired, it is possible to find the result of any cross. It takes time, logic and patience (or a computer).
It is in 1960 that appeared in Belgium the first Dos Pâles Bruns.
Let's try to understand how such a combination of colors could be born.
Brown and pale-back sex-related factors are known to be located on different X chromosomes and at different locations (loci): (1) and (2).
They are therefore not normally linked (otherwise all the browns would be pale as well: which is not the case).
How could they be linked on the same chromosome? (3)
When a brown male is paired with a pale gray - backed female (or vice versa), gray males with brown and pale backs are obtained each time. Each male therefore has two different X chromosomes: one carries the genes "brown" "not pale back", the other carries the genes "not brown" and "pale back". Being recessive, none of these genes can express themselves since it is in a single copy; being non-alleles, none can dominate the other; it is therefore a natural gray color that expresses itself.
How will these genes be transmitted by the male to his offspring ? To understand it well, some explanations are necessary.
Chromosomes are very long molecules (2 millionths of a millimeter thick, 5 cm of average length in humans) entangled, in normal times, 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 exactly identical chromatids attached to each other by a centromere.
Each chromatid then spirals. It is only then that the chromosome becomes visible under an optical microscope. The chromosomes cluster together and pair with each other in pairs.
During this phase, two chromatids of the two contiguous chromosomes can cross, break and then be joined together by exchanging more or less important segments. This is the so-called crossing-over phenomenon.
The "brown" gene could thus be linked to the "pale back" gene on the same X chromosome. A gray male with brown backs and pale backs can (but only in this way) produce pale gray, gray, brown backs and pale brown backs. (12.5% of each).
With this spanning, this same male could have also :
• Crossed with a pale-backed female: 12.5% pale gray-backed male with brown.
• Crossed with a brown female: 12.5% brown male with pale back.
By coupling one or the other of these with their sister "pale brown back", it is possible to obtain (in 3rd generation): 25% of pale brown backs and 25% of pale brown backs.
A : Normal
B : Contracted spiral
C : Schematized
We do not know if this is how the mutation actually appeared but the hypothesis seems likely. The brown masked that appeared at the same time in Great Britain may have had the same origin (a crossing between the chromosomes of a gray-backed gray-backed male with brown and brown can give females masked brown).
From the tip of the bill to the end of the tail: 11.5 cm.
Strong impression - Short and stubby size - Round head - Packed neck - Chest relatively wide and round.
The head, neck, back and tail should form a single line with a minimal hollow in the neck and at the intersection of the tail at the rump.
The curve formed by the rounded chest and the belly line should be regular from the throat to the anal area.
The dorsal line can not be crushed and the ventral line can not fall.
All parts of the body must be in harmony with each other.
Good round view on all angles - relatively wide front view - Must be in perfect harmony with the beak and body - Eyes placed about the center of the head, alive and dark colors unless the standard of the specified variety does not give it otherwise.
Short, relatively heavy and conical - Well implanted in relation to the rest of the head - Mandibles overlapping perfectly and of the same length. Mandibles crossed or too long are to penalize.
The bill can not be chipped or spotted.
In the male, it is coral red while in the female, it is red orange unless the standard of the variety specified does not otherwise describe it.
On the perch, half sitting without the belly feathers touching the perch, the legs being slightly bent.
The upper body slightly upright, the tail roughly in line with the line of the back. A falling tail will always be penalized. The wings tight to the body, touching the root of the tail without crossing or straightening. It is necessary to maintain a claim in a conformal cage, the bird being as little as possible in the bottom of the cage and also not attached to the bars.
Red orange unless the standard of the variety specified does not otherwise describe.
The legs, fingers and nails must be well formed, not damaged or spotted and without scales.
In perfect health, without deformations nor other infirmities.
Plumage very smooth, undamaged and complete. Sick, deformed or crippled birds do not have their places at exhibitions.
I made this glossary to illustrate in photos the mutations existing in the zebrafinch.
He can help you identify the mutation (s) of your zebrafinch.
Important clarification : To identify the genotype of your zebrafinch, it must be taken into account that a zebrafinch can carry a mutation without being mutant. Being a carrier (/) of a mutation means that it is partially present (genetically speaking). from a visual point of view the partially carried mutation will not be seen or only by some clues present in the appearance of the bird.
It will be necessary in this case, to have an eye informed to determine the genotype. Sometimes docking couplings will be required.
Your zebrafinch can also have several mutations, the possible combinations are numerous.
This glossary is based solely on the phenotype (visual characters) and simple mutations (not combined).
The gray zebrafinch is not a mutation, it is the original type (wild).