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Example of Inbreeding

AN EXAMPLE OF INBREEDING, how close is it really. By Graham PASCOE


Brother to Sister Matings, are considered by some to be the worst inbreeding you can do.


Remember that the cock and the Hen can only pass on, one half of all the chromosomes they carry, in effect that means that only one half of the cock’s, and one half of the hen’s, genes are passed on to their progeny, So that each young gets it’s allocation of two genes for all of its given features. Remember, 65% of all the genes the bird has are not there for colour size and type they are there to fight bacteria and viruses’ 


We now know that a Birds Chromosomes for sex determination are Z/Z for Males. And Z/W for Females.

This ZZ male and ZW female, is important when evaluating any sex linkage feature, either Dominant or Recessive, because that feature will only be present in the Z Chromosome, The Sex-linked Recessive feature also has another consideration, In that it has to be present in both Z Chromosomes in the male bird to be visible, but only in the one Z Chromosome to be visible in the female 


Homozygous, Heterozygous and Miosis, what do these words mean.


The worst condition you can get in your birds gene pool is a pair of genes that are homozygous for a bad fault. The best condition you can have is Homozygous genes for all the good features you want in you birds. 


Homozygous means gene pairs the same or alike, they contain the same DNA material; therefore no surprises in the outcome, what you see is what you get. The letter allocated to each gene is called an allyl, upper case “Z” for Homozygous meaning that no changes have been made to this gene. Lower case “z” for Heterozygous, meaning that changes have been made to this gene. So Z/Z is a Homozygous male bird for the Z gene, both of the “Z” genes are carrying the same material, “in most cases”. (Mutations are still happening. The process of dividing the chromosome into halves and there by producing the cells to be pass on is called Miosis, and if this process goes wrong, and a process called crossover occurs, then this will cause a variation, and ounce this happens, the progeny is carrying that variation and can pass it on, so remember it is not necessarily passed on by any of the parents carrying it). The alternative to Homozygous is Heterozygous, this is shown with allyl “z” and would make the male a Heterozygous one for the Z gene, Heterozygous means gene pairs not the same or alike, i.e. the lower case “z” infers that the chromosome, is carrying a feature that you do not see, It is more commonly known as “Split For” you may already know that a gene is changed, with good record keeping, and your knowledge of where the bird came from. The bird may be a Zebra finch and be split for Fawn, It would be written with Allyl’s like this “Z/zf “.


But if you do not know what the bird is carrying, the only way to find out is to test mate it to all the birds you think could be in its background, or that you suspect, could be in its background and study the progeny.


Remember it may show up in the first 5 but it could take 10, or more, or how ever many progeny, for an unknown gene to appear, to produce these numbers, foster out the young and eggs, it will take less time to get an answer.


Remember, we are talking about any gene on any chromosome, not just colour , size , type. Breeding ability is very high on my selection criteria.


On the subject of knowing what a bird is split for, what is the real need? If the bird qualifies in enough good points to breed with, then do it, you would have to put this bird to a bird that has the colour of the split. Or was split for that colour, for that colour too show up. The difficulty with all pairings, is you need to know about all the genes from both birds not just the genes for colour 


Why go on about Homozygous and Heterozygous? Because it has been argued for years that if you breed to close you will end up with a line of birds that are Homozygous, at the second filial generation in some cases, and if that line of birds has a bad fault in it, you will spend years trying to breed the fault out.


But if you only outcross, using Heterozygous birds, are you any better off? 


You do not know, what genes you have, or what genes you are passing on to the next generation, or you’re subsequent generations of progeny? There could be bad genes in every outcross; these genes become Homozygous then what. 

I will show you how the matrix system works. A matrix is simply a set of squares drawn to show the number of genes you are trying to study, the number of genes you study is up to you, the top row is always the cock and the first vertical row is always the Hen. Bear in mind Chromosomes do split in halves, these halves do contain half of the genes and DNA of the parent bird, and will be passed on, to all of their progeny, But the genes and therefore the DNA, do not get passed on in a numerical system; they are passed on randomly, in other words 1set of male genes from the same half of any of his chromosomes can be passed on to all the progeny in the same nest. Not as would be expected each half, passed on equally.


The matrix system works because it will show you all of the possible outcomes for any pair of birds, for any pair of genes, when you know what the birds are carrying in their gene pool. But not which nest they will appear in, I have mentioned how you have to test mate to know, what genes you have in the gene pool. An explanation of random genes being passed on is like the family of humans that only has boys or only has girls. The % of sexes produced should be 50% of each in theory.


This is a matrix of any pair of birds, and each bird is given a different number to make it easy to trace their breeding line. The cock bird (Father] is No. 1 and has the genes Z1/Z2, The Hen bird [Mother] is No.2, and has the genes Z3/W1.


First Mating

The progeny from this pair is the first filial generation. Numbered 3,4,5,6.


Let us try the brother /sister mating from the above birds. There is 4 combinations to try. No. 3 cock and No. 4 hen and No. 6 hen,

Then cock No. 5 and No. 4 hen as well as hen No. 6.

Only bird No. 7, 19, Are homozygous. Of interest is bird No.8 a copy of her mother No. 4 as is No. 12. Also birds’ No. 10, 14, 18, 22 are a copy of bird no2. Their grandmother. Birds no 11, 15 are a copy of their grandfather. Also of interest is the first mating of brother No. 3 to sister No. 4 you loose the Z2 gene. Similarly brother No. 5 to sister No. 6 you loose the Z1 gene. By doing this exercise you can compare and pick out the features you are looking for, and which line is producing the better features, so you would know you were on the right track.


We can now do the matrix on the matting’s Father to Daughter, Mother /Son most people consider these pairing, more line breeding than inbreeding.


And part of the reason for this attitude is the belief that, the inbreeding percentage, goes up after successive generations.


The first mating is 50/50 inbred percentage of the parent birds.


The first mating of father to daughter will produce 75% of the father and 25% of the mother. The third generation = 87% of Father and 13% of mother.


This is not true; let me show you how the matrix of father /daughter matings works. The original Pair.

All progeny are 50% of the father and the mother

Progeny No. 23 is 100% Homozygous, No. 25 is a copy of No. 1 the father. No. 24 is a copy of No. 4 her mother. No. 26 is a copy of No. 6 her Aunt.

Progeny No. 29 is homozygous. No. 27 is a copy of No. 1 the father. No. 28 is a copy of No. 4 her Aunt No. 30 is a copy of No. 6 her Mother.


If you continued this matrix of Father to the Daughters into the second generation you would find the outcome to be the same, the Hen birds No. 28, and 24, have the same genetic make up as hen bird No. 4, Likewise Hen birds No. 30 and 26 have the same genes as hen No. 6.


You will also note that in the Father/ Daughter matings genes Z3, are now lost. If Z3 is a gene that you did not want, then you have successfully taken it out of your breeding program.


This program does give you comparisons to see, this will give you quicker results if you use the relationships, with the good features.


What if you wanted Z3 genes though? What this is showing you, is a method of ridding your program of a gene you do not want, but remember if you want the genes from Z3 be careful how you use them, this also brings up the point, do not mate any birds until you have a three generation breeding plan in place. Set your self goals to be achieved.


Mother to Son Matrix. Use pair No. 1 as starting point.

Birds that are Homozygous, in Father Daughter matings are Birds No. 23, and 29, all from the father’s side. While the Homozygous birds in Mother to Son matings are birds No. 42, and 46, what is worth looking at is the homozygosity of No. 42, 46 it is all from the mothers side, if these birds are carrying the features you are looking for, and are better than the ones on the cock birds side, change your breeding program. The reverse of this is also valid. But again you will not have any “Z2” Genes, if you use either No. 42, or 46. So you would need to see a marked improvement in that progeny over the alternative to make it worth going on with.  Bird’s No. 43, 47 are copies of their mother bird No. 2.

There are advantages, with using the Father/ Daughter, and Mother /Son breeding programs, you can sort out which line is producing the features that you are looking for, and you can drop bad genes if you need.The only disadvantage is you have to do all of the possible matings to be able to compare the progeny, and thereby make an informed decision.


The problem with outcrossing as I see it is, you have got to make a choice at the second generation or at least by the third generation, which of the progeny up to that point, have the features you are looking for, if you now have some good birds, and there is no reason why you would not have, where do you go next, you will have to know a lot of breeders with good birds that can supply you with better out crosses, just to keep going.


One other point to be considered is do you know for sure who the father is. There is scientific proof now that a large number of birds are not monogamous, Zebra’s, budgies, canaries. Gouldian’s, Manikins’. To name a few, are very much promiscuous, the hens will, while courting a selected male accept advances from any male that fits her selection criteria. She will do this during courtship, and during egg laying. This applies to aviary breeding of course, not cabinet, or one pair per aviary.


So if you have more than one pair in the same environment you can never be sure who the father is.

Just going back to Miosis the chromosomes splitting in halves, there by making copies to be passed on to their progeny. A study done at a Sydney University, concluded the following. DNA from a selected site was taken from a two year old girl, this DNA was checked to see if the nuclei in the genes had any damage or changes. It was found to be intact. The same DNA was taken from her Father, the same checks made and it was found that 12% of them had been damaged. The same DNA was taken from his Mother, the same checks made and it was found that 25% of them had been damaged; the same DNA was taken from her mother, Great Grand Mother to the 2 year old girl. It was found that 47% of her Nuclei had been damaged. Conclusion, you will get more problems and variations out of old stock.

I have been able to get back a pair of Alumina, my own breeding, the pair consisted of a Grey/Alumina cock and an Alumina Hen. First nest, 2 Grey/Alumina and 2 Alumina. One Grey from first nest is a Hen a very good bird, I mated her back to her father, both split Alumina, First nest 3 Greys 1 Slate hen, second nest 2 Greys and 2 Alumina, the Greys and the Slate are only possibly split Alumina. The point being made here is first nest of Grey/Alumina to Grey/Alumina no Alumina produced. The whole outcome from 8 young = 25% Alumina produced theoretically should have been 50%, so the lesson is don’t give up too soon on what you expected the out come to have been. Keep on test mating.


I have completed a course on genetics at Tafe Collage Panorama.


We had to do breeding programs with mice, because you can get answers more quickly with the way they breed. And I have produced three generations brother to sister with no bad outcomes, only good ones.

And in my dealings with people from the bird world, I have been confronted with the question of inbreeding; my answer has always been. How many generation have you produced by using brother /sister, or father /daughter, or mother /son? The usual reply is none; it’s not good mating them together. They claim that they were told by some body, or that they had read it somewhere.


If you have not tried it then where is the proof.


By Graham PASCOE

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