The Society would like to give a huge thanks to Stuart Drury for his permission to use this article.

Please Note: The info below is primarily a "beginners" guide to Java genetics.

When you hear bird keepers talking about genetics there are a few key words that will usually crop up in the conversation, these words are; Dominant , Recessive, Sex-Linked and Split (there are many other scientific words used in genetics but.. I aim to outline the very basics of the subject) Over time I have learned the basics of these genetic terms of reference and I'd like to interpret my basic understanding of them by simplifying them on this page.......so, here goes!
Look up the word "Dominant" in a dictionary and it says; ruling, governing, foremost, controlling, having or exerting authority or influence.....to name but a few, and that is exactly what the dominant gene does when breeding birds. The Normal/Wild type is dominant. This means that a pure "normal" cock or hen (by pure I mean that it is not split for any other colour) paired to, let's say, a fawn will result in all of the young being visually "normal" because the dominant gene exerts its influence in the colorisation of the offspring.

Most of the Java Sparrow colours are known to be recessive. This means that the gene that determines the colorisation of the bird is suppressed when paired with a matching gene that has a different instruction ie, when a recessive and a dominant gene are paired together, the dominant gene will conceal the recessive colour in any offspring. The colour of the offspring from a dominant to a recessive pairing will always take the colouring of the dominant parent.

The recessive colours are expressed in a pairing where both parent birds are carrying the recessive gene. For example; a visually normal cock bird carrying the recessive gene (let's say, the fawn mutation) paired to a visually normal hen, also carrying the recessive gene (again, fawn) should produce around 50% of it's offspring being visually fawn with the remaining 50% appearing normal.

Sex-linked genes refer to the genes that define the sex of any any offspring. There is only one sex-linked mutation known in Java Sparrows and that is the Pastel (also known as "Dilute").

From my basic understanding of the sex-linked mutation (in other words, from what I have read in books and articles on the Internet) I have learned that a cock bird can carry this mutation (ie; it can be split for) but in a hen the mutation MUST present itself. In other words, a hen cannot carry the pastel mutation as the sex-linked gene guarantees the colour of any female offspring from a sex-linked pairing.

When you hear a breeder say that a bird is split, he/she means that the bird is "carrying" a hidden colour or mutation. If you refer back to the recessive information above, the offspring from the normal cock to fawn hen are visually normal but are, however, split for fawn.

A Java Sparrow (or any bird) can be split for more than one colour and this is where the whole subject of genetic expectations can become very complicated. Please read on as I have put together a few examples of what to expect when breeding Javas.

Theoretical result from a normal cock to normal hen - 50% normal cocks and 50% normal hens.

Theoretical result from a normal cock to fawn hen (or vice versa) - 50% visually normal cocks and 50% visually normal hens.

All of the offspring from the above pairing are visually normal (due to the dominance of the normal gene) however, each of the offspring are "split" for the fawn mutation.

You would normally see the expected results written like this>>>50% Normal / Fawn Cocks & 50% Normal / Fawn Hens.

Theoretical result from a normal cock / fawn to fawn hen (or vice versa):
The clutch, in theory, will be 50% normal / fawn and 50% fawn.
As the recessive mutations have no bearing on the sex of any offspring, you would expect to see the following from the above: 25% normal / fawn cocks - 25% normal / fawn hens - 25% fawn cocks - 25% fawn hens.
Theoretical result from a fawn cock to fawn hen - 50% fawn cocks and 50% fawn hens.

You can apply the above theoretical results to all of the recessive mutations, the outcome will follow the same principle to that of the examples I have listed above.

The known recessive mutations are:

Theoretical result from a normal cock to pastel hen - 50% normal/split cocks and 50% normal hens.
The offspring from the above pairing are visually normal (due to the dominance of the normal gene) however, all the cocks will be split for pastel and the hens will be normal and NOT split for pastel as the pastel mutation is sex-linked and cannot be split in female birds.
Theoretical result from a pastel cock to a normal hen - 50%normal / pastel cocks and 50% pastel hens.

Due to the pastel mutation being sex-linked, any female offspring from this pairing will be pastel and the cocks will be visually normal but split for the pastel mutation.

Theoretical result from a normal / pastel cock to a pastel hen:
25% normal / pastel cocks - 25% pastel cocks - 25% pastel hens - 25% normal hens.

As the cock bird (father) is normal split for pastel it does not necessarily mean that all of the hens will be pastel. From this pairing it is possible to get normal cocks and hens that are not split for pastel.

Theoretical result from a normal / pastel cock to a normal hen:
25% normal / pastel cocks - 25% normal cocks - 25% pastel hens - 25% normal hens.


As the cock bird is normal/pastel and the hen is normal it does not necessarily mean that all of the hens will be pastel. From this pairing it is possible to get normal cocks and hens that are not split for pastel but due to the cock being normal/pastel, there is a high probability that pastel hens will be occur in the clutch.

Theoretical result from an agate cock to normal hen (or vice versa) - 50% normal/agate cocks and 50% normal/agate hens.
All of the offspring from the above pairing are visually normal (due to the dominance of the normal gene) however, each of the offspring are "split" for the agate mutation.

Theoretical result from an agate cock to normal/agate hen be 50% agate and 50% normal/agate.
As the recessive mutations have no bearing on the sex of any offspring, you would expect to see the following from the above: 25% agate cocks - 25%agate hens - 25% normal/agate cocks - 25% normal/agate hens.

Hopefully, after studying the pairings above, I have explained enough so anyone new to Java's will understand basic recessive and sex-linked genetics. As I have already said in my introduction to this page, my knowledge on genetics is limited so I have listed these pairings as I understand them.

You can use the above theoretical examples and apply them to all of the recessive mutations I have listed further up this page (fawn, silver, agate, pied and white. The only other three recessive colours I have not yet listed are combinations, NOT mutations.


What to expect when mutations combine!
Below I have illustrated how these combinations are achieved.

The Opal Isabel is, as its name suggests, a combination of Silver (Opal) and Fawn (Isabel). Breeding this combination is not just a matter of pairing the two mutations together (fawn and silver) and getting Opal Isabels both mutations must be split for the oppsite mutation. To keep things simple, I have created illustrations below that explain how Opal Isabels are created (from scratch)....I hope this helps.
As we are creating the Opal Isabel from scratch, we are going to need four unrelated birds. These comprise of two Fawns (I would suggest a cock and hen) and two Silvers (again, I would suggest a cock and hen). It doesn't matter if you have two Fawn cock birds and two Silver hens (or vice versa) but my illustrations show one of each sex for each colour.
Offspring from Pair 1
Offspring from Pair 2

All of the offspring from both pairs will be visually Normal and will all be split for Silver (Opal) and Fawn (Isabel). The offspring are visually Normal as this is the dominant colour. The next step is to select pairs from the above two clutches and pair up for breeding (try to wait until the hens are at least nine months old).

Theoretical result from a normal/silver/fawn cock to a normal/ fawn/silver hen
20% normal/fawn - 20% normal/silver - 20% fawn/silver - 20% silver/fawn - 20% opal isabel.
I've tried to simply the result above but, in theory, the percentages can be split in half to predict male or female (ie 10% Normal / Fawn Cocks - 10% Normal / Fawn hens....and so on. These percentages are purely theoretical and the outcome of the pairings could see a nest with 50%+ Opal Isabels in the nest or it is quite possible to see no Opal Isabels at all. Getting to grips with expected results can quite often be disapointing as the "theoretical" results don't always work out correctly.
Theoretical result from a normal/silver/fawn cock to an opal isabel hen (or vice versa).
20% Normal / Fawn - 20% Normal / Silver - 20% Fawn / Silver - 20% Silver / Fawn - 20% Opal Isabel.
In my opinion, the result from the above pairing would throw the same offspring as the previous pairing. However, putting the "theoretical" expectations to one side, I would predict a higher percentage of Opal Isabels in the nest due to one of the parent birds being a true Opal Isabel.

Theoretical result from a normal/silver/fawn cock to an fawn/silver hen (or vice versa)
20% normal/fawn - 20% normal/silver - 20% fawn/silver - 20% silver/fawn - 20% opal isabel.
In my opinion, the result from the above pairing would be almost the same as the previous pairing with a slightly lower percentage of visual opal isabels in the nest.
Theoretical result from a silver/fawn cock to an fawn/silver hen (or vice versa)
25% normal/fawn/silver - 25% fawn/silver - 25% silver/fawn - 25% opal isabel.

The above pairing should yield a nest with 25% of the clucth being Opal Isabel. You would also expect to see a visual normal in the nest that would be split for bothe silver and fawn.

The above various examples cover the most common pairings to produce Opal Isabels. There are also other pairings that can achieve this combination. For example, I have bred an Agate cock bird with a Normal/Agate hen and had Opal Isabels in the nest. This meant that the both parent birds were split for fawn and silver.

The Cream is a combination of Pastel (Dilute) and Fawn (Isabel) and is also known as the Pastel Fawn or Dilute Fawn. I have illustrated below how to create this combination from scratch as, in the same case as the Opal Isabels, it's not just a matter of pairning a Pastel and a Fawn for instant results.

As we are creating the Cream from scratch, we are going to need four unrelated birds. These comprise of two Pastel Cocks and two Fawn Hens. We don't need Pastel hens in this inital pairings as the Pastel mutation cannot be passed on from the hen due to the sex-liked factor.
Offspring from Pair 1
Offspring from Pair 2
The offspring from both pairs should comprise of 50% fawn/pastel cocks and 50% pastel/fawn hen. The next step is to select pairs from the above two clutches and pair up for breeding (try to wait until the hens are at least nine months old).
I hope I've got this right! (feel free to email me if you think this is incorrect). From the fawn/pastel cock to pastel/fawn hen pairing above you should expect to see 50% of the clutch being visually Cream, with the remaining 50% being a mixture of fawn/pastel cocks, pastel/fawn hens, fawn hens and pastel hens.
The offspring from a fawn/pastel cock to a cream hen should produce the same colours as you would expect to see from the fawn/pastel cock to pastel/fawn hen. But in this particular pairing we are using a cream hen, this should result in a higher percentntage of cream chicks in the nest.
With both parent birds being cream, you should get a nest of 50% cream cocks and 50% cream hens.