General genetics

General genetics

By Inge Fagerli


	This information is available in so many articles directed at pigeonfanciers, so I will not dive too deeply into these matters. It is important that the reader, you, have general knowledge of the terminology used regarding genetics when reading the other articles posted here. Therefore I will briefly go through the basics of genetics before moving to the other, far more interesting subjects later. Of course if you know some genetics you may skip this article.

Genetics are the base, or core, of heritage. All pigeonbreeders are involved with heritage or how else can we anticipate the qualities of offspring? We pair our pigeons regarding to several theories. Some of these may be "eyesign" or "anatomy" or "wing theories" or "hybrid vigour", but I will not discuss these here, nor will I discuss whether these can be rightfully termed as theories. The reason I avoid this discussion is lack of knowledge and understanding of many of these "theories", and the fact that this discussion really doesn't belong here. Perhaps later I will publish my views on some of these themes, suffice to say at this time, that Mattacchione's articles are much in line with my thinking.

The choosing of breeders is a matter of selection. How do we choose which birds to pair up? Some practice "best-to-best" pairing. What is "best"? Again it takes us back to selection, doesn't it? I say that; "when pairing pigeons for breeding of specialised birds, you shall breed the pigeons most likely to produce superior offspring together to each other". You say; "I know that". So which birds are most likely to produce superior offspring together? Back to genetics, no?

Well then. We agree. You start to feel that I am wasting your time. Maybe I am. Perhaps I wrote this article with the intention of weakening my competitors by making them read garbage instead of taking care of their birds.

Some traits, characteristics, are dominant and some are recessive. This depends on which traits are compared to which. Chequered is dominant to barred which is dominant to barless. Barless is recessive to barred which is recessive to chequered. Some genes aren't dominant or recessive with regards to each other. Some traits are passed of intermediately, which means that the offspring gets the mean expression of both parents. Some traits are unrelated and will express themselves regardless of the other. Some traits are dominant and expressed accumulative, which means that the expression is stronger in homozygotes than in heterozygotes.

All traits are controlled by genes, but most are controlled by more than one gene, and often we don't know exactly which genes are involved with the trait. Homing ability is such a trait.

Genes are located on the chromosomes and they are always located as pairs. (Well not always, but most of the time). Now the matter of dominance comes to play. We call the location of a single gene, a locus (pl. Loci), and genes are located as pairs on the loci. This way, we have two genes of the same kind or two genes of different kinds on the chromosomes. Two of a kind is called homozygous (AA) and two kinds are called heterozygous (Aa). If a trait is expressed as heterozygous a dominant gene will override the recessive gene.

Pigeons that are homozygous for a special trait is said to be "true breeding" for that trait. A barless pigeon will always pass along the gene for barless, whereas a chequered pigeon may pass along the gene for barred if it is a heterozygous chequer.

With expression of recessive traits you can always tell that the pigeon is not carrying any genes dominant to that trait. It is harder the other way around. How could you check if a chequered pigeon is homozygous for chequer? This is difficult to prove, but if you breed the chequer to a barred, and get barred offspring, the chequer is certainly heterozygous.

Are genetics like these important to the breeder of racing pigeons? Not very, but the principles are the same for any type of trait and I choose to use familiar examples.

Steven van Breemen talks about "the dominant breeder". This is a true breeding type of bird. He uses the expression regarding a pigeon that gives many of its traits along to its offspring, thereby dominating the genetic expression. No parent can ever pass more, or less, than half its genetic material on to its offspring. The dominant breeder must therefore be a bird with strong genetic makeup, so strong that it will dominate the genes passed on by the other parent. This will be pigeons which are homozygous on many loci of importance for breeding ability. There has not been done much research on this topic, and racing ability is controlled by several loci. We don't know how many loci that are involved with racing ability, and so we don't know how much we actually know.

What we need to do to breed pigeons with certain characteristics, is to breed all the traits we consider important together into one bird. We also want to be able to reproduce this bird on demand. How can we make this possible?

Well, back to pattern. We have one chequered bird and one barred bird in our loft.. We decide that we want only barred birds in our loft.

We breed the barred to the chequered, but get only chequered offspring. Well, the chequer is probably homozygous for that pattern. (Most chequered are heterozygous, but this is not relevant here). The offspring from this cross will be heterozygous for chequer and bar. We take one of the offspring and breed back to the barred parent. The barred parent will pass on the gene for bar, and the other parent will pass on the gene for bar half the time. So half the offspring from this mating will be barred. At this time it would be wise to remove the birds that are chequered, since barred birds was what we wanted. The technique used here is a back cross (offspring paired with ancestor within a line), but you could use any blue bar other than the parent. You see now that we achieved the homogeneity within the populations pattern within two generations. We use f to symbolise offspring and f1 to symbolise first generation and f2 to symbolise second generation and so on.

Now we decide that we want barred pigeons, but we don't want blue bars, we want red bars. Now what?

We get an ash red bird. Pattern isn't very important, but it saves time, one generation, if the bird is red bar. Breed this bird to a blue bar and we get some reds. (Colour is special, since it is sexlinked, but we'll ignore that for now). Red is dominant, and the first generation of offspring will be heterozygous for red colour.

Now it is wise to breed this offspring back to the red parent, while selecting against blue colour. That way we will get some homozygous individual, true breeding, for red bar. How do we know which offspring is heterozygous and which are homozygous from this cross? Firstly, we didn't get any blues when crossing red into the line. If we had, we would know that the red parent was heterozygous. Certainty about homozygousity of dominant traits is normally not possible, but we can be increasingly sure by selecting against blue birds consistently.

However since red is sexlinked we can make sure that the birds are true breeding in an other way. Sexlinked means that the loci for this trait is located at the sex chromosome. In humans females are XX and males are XY. Birds are special in this regard. Males are XX and females are just X. So if we assume that the red bird is a hen, we know she only delivers red colour to her sons. Is this clear?

Every sexcell produced by the cock contains one X chromosome. Sexcells from the hen contains either X or not. Those that doesn't contain X become daughters, since they only get the X delivered by the cock. So any red birds from a cross between one blue bar cock and a red bar hen, will give red males and blue females. So we select against hens.

One cock (heterozygous) is put back on the mother. Now half the daughters will be red as will all the sons. Some of these sons (i.e. half) will be homozygous for red colour. The daughters will be true breeding for their colour. Again we select against blue colour.

If we put red brothers on red sisters, we get some cocks that occasionally produce blue hens. Those cocks should be selected against. In time blue colour will be "eliminated" from the population.

Now we have bred forth red barred birds, eliminating chequer and blue on the way. Is the process clear? We start from somewhere, with birds that show certain traits. We eliminate some and introduce others. This is possible to achieve simply by consistent selection, which is the preferred method by many fanciers, but controlled breeding saves a lot of time.

By understanding and applying principles of genetics and heritage it is possible to breed pigeons with higher levels of consistency and direction.

In our breeding lofts we want true breeding birds. How to achieve this is by selection and controlled breeding.

In the example above we shaped a population towards our ideal. We call this structuring the population. Structure will be the next topic I'll discuss in an upcoming article.