How to recognize a male split of black chest mutation


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.

Tear line

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 fine

- Tear line is present and wide :

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.

extension of cheeks black chest extension of cheeks black breast neck


Split (/) black chest : The drawing of the cheek will be irregular and one will generally observe an overflow of it up.

High Cheek Extension split Black Chest

In some cases the black breast split may have a cheek identical to a gray one. In this case, it will be necessary to rely on other possible clues.

4. Chin, throat and chest

Black chest : The most intense black possible rising as high as possible towards the chin.

chin throat and chest black chest

It should be noted that the zebras are no longer present.

Split black chest (/) : The chest bar will generally be wider than a gray; The welts from the beak to the chest bar will be present.

chin throat and chest black chest

5. Drawings of the flanks

Black chest : Uniformly lined with elongated white dots.

Black chest flanks

Split (/) black chest  :Uniformly garnished with white dots ranging from round to elongated.
To mark, here are the flank points of a gray :

Points of the flanks of a gray

The design of the sides slightly elongated or having an imperfect round shape will not be a sufficient clue. This can be part of a defect in gray (not split).

6. Drawings of flight feathers

Black chest : Remiges and secondary and tertiary wing coverts bordered by a brown and orange brown border.

Black Breasted flight Drawings

Some black breasts may not have these lines according to the level of selection made by the breeder.

Split (/) black chest : We can observe on some split remiges having more or less the above described drawing. Here too, the “force” of expression of the mutation will play its role.

Flight feathers of a gray

7. Drawings of the rectrices

comparison rectrices drawings

In a gray the design of the rectrices should be strictly horizontal and rectilinear.
In the 2nd case, "Grey split black chest", you can be between the defect of the rectrices of a gray or a black chest. It is therefore necessary to be careful and not to assert an analysis without taking into account the whole of the bird.
Finally, 3rd case, the black chest will have this drawing going towards the end of the tail, (oriented in the direction of the pen). Some split black breast may also have more or less this characteristic.


If one or more of these clues clearly altering one of the drawings is convincing on your zebrafinch, its genotype includes the black breast mutation. However, let’s be careful, other mutations can also interfere in the interpretation of the phenotype.

Among the split subjects you will find a lot of intermediaries. Which will be more precisely, between the phenotype of a gray :

Zebra finch male gray strain English

And that of a gray black breast :

Male Black Breasted Gray Zebra Finch

The black chest split will be positioned as an intermediary on all the drawings or on only a few of them (See the case of the split example below).
In other cases, the least detectable, the bearer of the black breast may have the phenotype of a gray (that is to say without evidence revealing the black breast mutation).
In the latter, only a verification by coupling can give you certainty.

Example of split black chest :

Diamant mandarin gris porteur poitrine noire

Evidence of black breast mutation :

- Very fine line of tears.
- Cheeks overflowing upwards.
- Presence of edging in the remiges.
- Drawing of elongated flanks.

Evidence that it is a split of the black breast mutation (non-mutant) :

- The zebras are present.
- The design of the rectrices remains that of a gray.

To resume what I observed while breeding black breasts.
Among the split born of couplings gray x gray black chest, gray/black chest x gray/black chest or gray black chest x gray/black chest, some showed a phenotype definable according to their proven genotype and others (rarer) could have the phenotype of a gray or very close to it. It can therefore be said that certain zebrafinch with a gray phenotype can be genetically carriers. Conversely, one must avoid confusing the defect that a gray may have with a gray split the black breast mutation.

The phenotype gives us interpretable indications, the exercise being difficult, hasty generalities or affirmations may seem unreliable. A conscientious breeder and experienced in the mutation, with a keen eye, will be the best able to translate the phenotype of a possible split of black breast or better still will be tracing the genealogy of a bird coming from its strain.

To identify a split of the black breast mutation, it is therefore important for me to have precisely in mind the phenotype of a gray and that of a black breast, to know all the modifications that implies this mutation. Knowledge of each point of detail will bring you or advance you to the answer.

Tony Lombard, amateur breeder of selection.
Article published in 2020.

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recessive Grey Selection Drawing split Mutation genotype phenotype Black breast