Genetics can be a very complicated subject to understand. As I have stated many times, I am not an expert and when it comes to genetics I hold my hands up to say that my knowledge is somewhat limited. I've written this page to try and simplify the genetic inheritance of Java Sparrows and I've listed a handful of example pairings.
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!
What does “Dominant” refer to in genetics?
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.
What does “Recessive” refer to in genetics?
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 i.e., 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 its offspring being visually Fawn with the remaining 50% appearing Normal.
What does “Sex-Linked” refer to in genetics?
Sex-linked genes refer to the genes that define the sex of 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 (i.e.; 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.
What does “Split” refer to in genetics?
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 Java’s.
Disclaimer: I am not an expert, this information has been gained through several years of my bird keeping hobby.
Normal Cock to Normal Hen
Theoretical result from a Normal cock to Normal hen - 50% Normal cocks and 50% Normal hens.
|Normal Cock to Fawn Hen (or vice versa)
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
Fawn Cock to Fawn Hen
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:
Normal Cock to Pastel Hen
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.
Pastel Cock to Normal Hen
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.
Normal/Pastel Cock to Pastel Hen
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.
Normal/Pastel Cock to Normal Hen
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.
Agate Cock to Normal Hen
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.
Agate Cock to Normal/Agate Hen
Theoretical result from an agate cock to Normal/agate hen 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!
The following pages explain how these are created.
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 Isabel’s both mutations must be split for the opposite mutation. To keep things simple, I have created illustrations below that explain how Opal Isabel’s are created (from scratch)....I hope this helps.
We need 2 unrelated Fawns and 2 unrelated Silvers
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.
The result of the 2 parings are as follows...
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).
So, to breed Opal Isabel’s we need to take a Normal/Silver/Fawn Cock from Pair 1 and a Normal/Silver/Fawn hen from Pair 2...
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 (i.e. 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 Isabel’s in the nest or it is quite possible to see no Opal Isabel’s at all. Getting to grips with expected results can quite often be disappointing as the "theoretical" results don't always work out correctly.
Other Pairings That Can Create Opal Isabel’s...
Normal/Silver/Fawn Cock to Opal Isabel hen
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 Isabel’s in the nest due to one of the parent birds being a true Opal Isabel.
Normal/Fawn/Silver Cock to Fawn/Silver Hen
Theoretical result from a Normal/Silver/Fawn cock to a 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 Isabel’s in the nest.
Silver/Fawn Cock to Fawn/Silver Hen
Theoretical result from a Silver/Fawn cock to a 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 clutch being Opal Isabel. You would also expect to see a visual Normal in the nest that would be split for both Silver and Fawn.
The above various examples cover the most common pairings to produce Opal Isabel’s. 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 Isabel’s in the nest. This meant that the both parent birds were split for Fawn and Silver.
Cream (Pastel Fawn)
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 Isabel’s, it's not just a matter of pairing a Pastel and a Fawn for instant results.
We need 2 unrelated Pastel Cocks and 2 unrelated Fawn Hens
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).
So, to breed Opal Isabel’s we need to take a Fawn/Pastel Cock from Pair 1 and a Pastel/Fawn hen from Pair 2...
The offspring from these pairing should be as follows...
Other Pairings That Can Create Creams...
Fawn/Pastel Cock to Cream Hen
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 percentage of Cream chicks in the nest.
Cream Cock to Cream Hen
With both parent birds being Cream, you should get a nest of 50% Cream cocks and 50% Cream hens.
I hope you have found this basic guide useful. I am not, by any means, an expert in this area but my knowledge has been gained over several years of bird keeping and by experiences shared by fellow enthusiast within the JSSUK.