|Autosomal Recessive Mutations of the zebra finch available in UK/continental Europe|
|Black Breasted||Recessive Cream|
|Orange Breasted||Yellow Beak|
Some of the listed mutations have been established in the UK for many years, and are frequently to be seen on the show bench. Many more were first established in Continental Europe, and have only in the last decade been imported and established in the UK. A number of people have been attracted to zebras having a combination of several of these mutations in one bird. One example is the phaeo, which is more strictly speaking a blackbreasted fawn isabel.
In the earlier articles, it was said that for the dominant mutations, if the mutation was present it must be there visually; whereas for the sex-linked varieties, in the hen it must be visual if present, but in the cock it can be visual or in hidden (split) form. In the case of recessive mutations it can be there in both visual or split form for both cock and hen. Another difference between the dominant, sex-linked and autosomal recessive mutations, is that in the case of the autosomal recessive the gene has to be present (in visual or split form) in both parents for that mutation to appear in the offspring. On the other hand it is amazing how often a visual recessive pops up in a nest from adults showing no trace of the recessive mutations characteristics. There is in fact no big mystery why this happens, as will be illustrated below. Let us take the example of a pair comprising a normal grey penguin and a standard normal grey. Which is the cock and which the hen is in this case immaterial, since neither mutation is sex-linked. The expectations from this pair are:
normal grey x normal grey penguin = normal grey/penguin cocks and hens
The chicks will thus all appear as visual normal greys, but will be split (carriers) for penguin; no visual penguins will appear. Taking one of these chicks and subsequently pairing it to another normal grey penguin will now generate some visual normal grey penguins, together with more splits:
normal grey/penguin x normal grey penguin = normal grey penguin + normal grey/penguin cocks and hens
In this case there should be approximately 50% each normal grey penguins and normal grey/penguins.
An alternative pairing, in the absence of an unrelated normal grey penguin, might be to pair two of the normal grey/penguins together. Again, because both birds have the penguin gene, albeit in hidden form, a small proportion of penguins will be produced:
normal grey/penguin x normal grey/penguin = 25% normal greys, 50% normal grey/penguin, and 25% normal grey penguin cocks and hens
The problem now arises that 75% of the youngsters will be visually normal greys, but only 2 out of three will carry the penguin gene, the other will be a pure normal grey! Now supposing you take one of the normal grey/penguin birds and perhaps hoping that it a pure normal grey use it in a breeding programme to produce normal greys, you might get the following:
Normal grey/penguin x normal grey = normal grey + normal grey/penguin cocks and hens
In other words, all the chicks will be visually normal greys, but some will also carry the penguin gene. This mating can be reproduced over many generations, until by accident you actually pair two normal grey/penguin birds when out will pop 25% normal grey penguins. Of course, by this time you may have forgotten that you ever used a bird with penguin blood in this line of normal greys! This is usually the explanation for the surprise appearance of a recessive mutation in a nest.
Table 2 contains a summary of matings which are most frequently used in the production of these recessive mutations. In Table 2 AR has been used to represent the autosomal recessive mutation where pairings involve the same mutation and a special case where the mutations are two different ones, the
two mutations have been designated AR1 and AR2.
It was earlier mentioned that many people want to breed zebras with a combination of recessive mutations, so how do you go about this? The first important requirement is patience! Let us say that you want to combine the blackcheek and blackbreasted mutations. The first step might be to pair a blackcheek normal grey to a blackbreasted normal grey:
Blackcheek normal grey x blackbreasted normal grey = normal grey/(blackcheek and blackbreasted) cocks and hens
|Pairings to produce autosomal recessive zebra finches|
|AR x AR||
= 100% AR cocks and hens
|AR x Normal Grey||100% normal grey/AR cocks and hens|
|AR x Normal Grey/AR||
= 50% AR cocks and hens
|Normal Grey/AR x Normal Grey/AR||
= 25 % AR cocks and hens
|AR1 x AR2||= 100% normal grey/AR1 & AR2 cocks and hens|
(where AR1 and AR2 are different autosomal recessive mutations)
So, starting off with two different pure recessive mutation parents, the first result is to produce visual normal greys! Such a result must have been a major disappointment to beginners and novices in the past, and here is where the patience factor comes in. What to do next? One possibility is to pair one of the normal grey/(blackcheek and blackbreasted) youngsters with another normal grey blackcheek or normal grey blackbreasted. This will give (in the case of the blackcheek being the chosen partner) a mixture of blackcheek normal greys, half of which would be split for blackbreasted, and normal grey/blackcheek again half of which would be also split for blackbreasted. How do you tell which birds have both blackcheek and blackbreasted genes? There are often small signs which enable an experienced fancier to detect, with good probability, which is which, but this is often difficult for the newcomer. But suppose you can detect which of these second generation is the desired blackcheek normal grey/blackbreasted, pairing two such birds together yields in the third generation 25% blackcheeked blackbreasted normal greys. The other 75% will all be blackcheeked normal greys, 2 out of 3 of which will also be split for blackbreasted.
An alternative route would be to pair two of the normal grey/(blackcheek and blackbreasted) birds together. This can give the desired result in the second generation (since both parents now have both genes), but the probability is one in sixteen (6.25%), which actually is the same as the other route above.
Once you have bred the desired combination, numbers can be increased by pairing it to another blackcheeked blackbreasted bird, or if one is not available, a normal grey/(blackcheekd blackbreasted). The first pairing will then give you 100% of the desired youngsters, and the second about 50%.
Clearly, you could then go on and incorporate a third recessive mutation, to give (for example) orange breasted blackcheeked blackbreasted normal greys, but I think it will be apparent that this will need to be done over several generations, and the wastage rate will be very high. Nevertheless, a few dedicated fanciers have put in the necessary effort needed to achieve it.
Although I have concentrated on the grey series for the purposes of the above examples, it is possible to do a similar thing in the fawn series. For instance, by combining isabel with blackbreasted fawn we can generate the blackbreasted isabel, commonly known as the phaeo, and further combine this with orange breasted fawn to ultimately give the orange breasted phaeo. It is then possible to further combine this with the dominant blackfaced gene to give a zebra genetically described as blackfaced blackcheeked blackbreasted isabel. The cock of this combination is quite near to pure orange, with no trace of black in its plumage!! Some of the interesting effects arising from incorporation of certain of the recessive genes on the visual appearance of zebras might form the subject of a future article.
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