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Breeding Recessive Mutation Zebra Finches

17 06/08 | 18:37

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Previous articles in this series dealt with the breeding expectations of zebra finches of the dominant and

sex-linked mutations. By far the greater number of zebra finch mutations fall into the group known as

autosomal recessive. Table 1 shows the list of these presently available in Europe; there are some others,

notably in Australia, which are not available to us. Even within this list, there are some which are not

readily available in the UK. For example, the recessive silver and cream seem to have disappeared from

the UK, having in the past been bred in good numbers, and there may only be isolated examples of the

agate and eumo.

Table 1.

Autosomal Recessive Mutations of the zebra finch

available in UK/continental Europe

Agate Penguin

Black Cheek Pied

Black Breasted Recessive Cream

Eumo Recessive Silver

Isabel White

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:

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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

Table 2

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

50% normal grey/AR cocks and hens

Normal Grey/AR x Normal Grey/AR

= 25 % AR cocks and hens

50% normal grey/AR cocks and hens

25% normal grey cocks and hens

BUT

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

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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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