THE USE OF GENETICS IN BREEDING CHAMPIONS
Almost two years ago I wrote two articles on Mendelian Laws. The feedback that I received was not too good and I realized that I needed to gain much more knowledge about genetics before I try to write anything on the subject again. The more I read, the more did I realize how little I knew and how vast the field of genetics is. At times I almost gave up my efforts – there was, and still is, so much to learn, and there is no guarantee that a breeding programme based on genetics will necessarily produce better results than just following your instincts. But curiosity got the better of me and I carried on. The original two articles grew into approximately 17 articles.
I feel that I am now ready to share my ideas on genetics with you for two reasons. Firstly, I hope that those of you who can will criticize and add to my ideas, so that I can learn more. Secondly, it would be really great if some of you benefit from the approach and breed top quality racers. I am now following the breeding system that I will describe in this series of articles, and you are most welcome to use any ideas that you feel might make a positive contribution to your own breeding efforts.
I asked a number of
experts in genetics to read and comment on my articles before I offer them for
publication. I would like to thank Alan Wheeldon (USA), Mauricio Jemal (
Dr Jaap Nel. Tel no (012) 653 2119. Fax no: (012) 653 7030. Email: firstname.lastname@example.org.
The 2005 Sun City Million Dollar Pigeon race will probably be remembered for the severe hiding that the South African pigeons got. I always thought we would do something to ensure that we will, eventually, beat the foreigners who dare to challenge us on our own home ground. Sadly we seem to be falling more behind every year. As always there are many different theories why this is so. The following are some that I heard during and after the race:
We no longer have the pigeons that can race well in overnight races. Because of our racing programmes, which favor shorter and good weather races, we cull all the tough pigeons, so that our pigeons can no longer keep up with especially the German pigeons.
The molting story still prevails – European pigeons molt between October and December, and ours between February and April, so that our pigeons compete with old and worn primaries.
January is not our racing season, so that our pigeons suffer from something similar to jet lag. They simply are not prepared for the races, both physically and mentally.
SA Pigeon fanciers prepare their pigeons well for races when they race from their own lofts. The moment their champions are raced by someone else, they simply cannot compete.
SA Pigeon fanciers dope their pigeons, thus creating a false perception of the quality of their pigeons in their own minds, so that they enter poor quality pigeons.
Foreign fanciers breed specifically for the MDPR, and we don’t.
proven racers, which are six months and older once they arrive at
All of the above might contain elements of truth. Point is, the only sure way in which we can increase the chances of
our pigeons performing well at
There is so much genetic terminology that it is difficult to follow articles on the subject. The development of specific terminology has an important function, as it permits single, descriptive words to replace cumbersome explanations. (Van Vleck, et al, 1987: 8). Still, one sometimes gets the impression that geneticists deliberately use technical jargon and complicated sentences to make their discipline appear more complicated than it really is. Take, for example, the following sentence: “ If bent sperm are present in large numbers, there is a problem with the osmolarity of the diluent as the sperm are approaching senescence.” (???)
I tried to rewrite the concepts and processes of genetics in more user-friendly terms, but was not able to remove all technical terms for obvious reasons. Because of this I will do my best to explain terms and concepts where I cannot replace them with more familiar pigeon terms and concepts. Then again, the serious pigeon breeder will make an effort to familiarize himself with terms such as phenotype and genotype. Still, don’t let the terminology put you off from learning more about genetics. The more you read and use the terms, the more familiar will they become and the easier it will be to understand and use them.
These articles on genetics focus on racing pigeons. Consequently definitions, processes and consequences are discussed in terms of racing pigeons. This does not mean that other living organisms (plants, animals, human beings) are excluded from them. In fact, most research has been done on living organisms other than racing pigeons. The reason for this ‘closed system’ approach is for the sake of simplicity and relevance. After all, we are interested in racing pigeons and how we can use genetics to breed top class racers.
Genetics is the study of the function and behaviour of genes. Genes are bits of biochemical instructions found inside the cells of every organism from bacteria to humans. Offspring receive a mixture of genetic information from both parents. This process contributes to the great variation of traits that we see in nature, such as the colour of a flower’s petals, the markings on a butterfly’s wings, or such behavioural traits as perseverance or speed in racing pigeons. Geneticists seek to understand how the information encoded in genes is used and controlled by cells and how it is transmitted from one generation to the next. Geneticists also study how tiny variations in genes can disrupt an organism’s development or cause disease. Increasingly, modern genetics involves genetic engineering, a technique used by scientists to manipulate genes.
Since the earliest days of plant and animal domestication, around 10,000 years ago, humans have understood that character traits of parents could be transmitted to their offspring. The first to speculate about how this process worked were probably the Greek scholars around the 4th century BC, who promoted theories based on conjecture or superstition. Some of these theories remained in favour for several centuries. The scientific study of genetics did not begin until the late 19th century. (Encarta, 2004: 2.)
Today we know that all plants and animals are composed of cells. Each cell contains a nucleus floating in the cellular fluid. Within the nucleus are some very special filaments known as chromosomes, which carry in a pre-determined sequence the genes, which contain the chemical substances involved in the transmission of hereditary traits. Genes are the units of heredity. Each animal species possesses a specific number of chromosomes; the pigeon has eighty. Chromosome numbers is not related to an organism’s level on the evolutionary scale, as some relatively simple organisms have large numbers of chromosomes and others small numbers. The chromosomes are arranged two by two, so the pigeon therefore has forty pairs of chromosomes. Each pair of chromosomes has a characteristic appearance and shape (long, short, thick, thin, stick-like or curved) enabling a specialist to recognise them. The two chromosomes of a pair are known as homologous chromosomes. Even though the homologous chromosomes have the same external appearance, they are not identical. Remember:
Chromosomes come in pairs as do their corresponding genes, these gene pairs reside at specific locations on the chromosomes (known as loci).
For each gene pair an individual gets one gene from each of its parents.
For each locus there may be a number of alternative genes available within the gene pool (each alternative is known as an allele and codes for a slightly different version of the same protein).
While the gene pool may have with a number of alleles for a given locus, the individual has either 1 allele (the homozygous case where both genes are the same) or 2 alleles (the heterozygous case where the two genes are different).
The genes carried by a chromosome may be different from those on its homologue from a purely genetic point of view; the alternative forms by which a gene may manifest itself are also known as alleles. There are generally a number of slightly different genes that code for forms of the same protein, and fit into the same locus. Each locus, then, will have one allele from the mother and one from the father.
The modern science of genetics influences many aspects of daily life, from the food we eat to how we identify criminals or treat diseases. In pigeons racing, we hope to alter the pigeons to breed (or be) better racers. This can include modifying the genetic composition of the pigeons to better withstand diseases or to perform well in racing, hopefully at an earlier age.
The site where genes work is the cell. Some organisms, such as paramecia or amoebas, are made up of a single cell. Other organisms are made up of many kinds of cells, each having a different function. For instance, a pigeon contains some cells that form the feathers and other cells that form the body structure. Each cell’s function within an organism is determined by a subset of the genes contained in its nucleus. Remember that each cell has the total genetic code for the organism, so those loci that code for other cell types are “turned off”.
Genetic information is encoded and transmitted from generation to generation in deoxyribonucleic acid (DNA). DNA is a coiled molecule organized into structures called chromosomes within cells. Segments along the length of a DNA molecule form genes. Genes direct the synthesis of proteins, the molecular labourers that carry out all life-supporting activities in the cell. We know that protein is a physical component of the body such as the protein that occurs in a feather. However, what I am referring to here is protein as used in organisms as enzymes that control the biochemical reactions that drive everything done in a living entity from the contraction of a muscle to the digestion of food. The proteins produced may be structural or they may be enzymes that facilitate chemical reactions in the body.
Although all pigeons share the same set of genes, individual pigeons can inherit different forms of a given gene, making each pigeon genetically unique.
DNA has a shape rather like a corkscrewed ladder. The “rungs” of the ladder are of four different types. The information on DNA comes in how those types are ordered along the molecule, just as the information in Morse code comes in how the dashes and dots are ordered. The information in three adjacent rungs is “read” by a kind of ribonucleic acid (RNA) that hooks onto a particular triad of rungs at one end and grabs a particular amino acid at the other. Special triads say “start here” and “end here” and mark off regions of the DNA molecule we call discrete genes. The eventual result is a chain of amino acids that makes up a protein, with each amino acid corresponding to a set of three rungs along the DNA molecule. There are also genes that tell the cell when to turn on or turn off another gene.
Fine, now we know that chromosomes are essentially DNA molecules. In an advanced (eukaryotic) cell, these chromosomes appear as threadlike structures packaged into a more or less central part of the cell, bound by a membrane and called the nucleus. What is more important is that the chromosomes in a body cell are arranged in pairs, one from the father and one from the mother. Further, the code for a particular protein is always on the same place on the same chromosome. This place, or location, is called a locus (plural loci).
Organisms could not grow or function properly if the genetic information encoded in DNA was not passed from cell to cell. Remember that DNA is packaged into structures called chromosomes within a cell. Every chromosome in a cell contains many genes, and each gene is located at a particular site, or locus, on the chromosome. The number of homologous (pairs of) chromosomes in a cell depends upon the organism – for example, most cells in the human body contain 23 pairs of chromosomes, while most cells of the fruit fly Drosophila contain 4 pairs. As I already mentioned, pigeons have 40 pairs of chromosomes. So, in pigeons (like in most other living organisms) chromosomes exist in matching pairs, with the exception of sex chromosomes. One sex has all matching pairs whereas the other sex has one chromosome pair that does not match. In mammalian species, the male has an unmatching pair; in avian species, the female.
When a pigeon makes an egg or a sperm cell (collectively called gametes), the cell goes through a special kind of division process, resulting in a gamete with only one copy of each chromosome pair. The selection of which allele winds up in a gamete is strictly random, unless two genes are very close together on the same chromosome. We will return to this when we discuss the phenomenon of crossover. Thus, a pigeon that has one gene for blue and one for red may produce a gamete, which has a gene for blue or red pigment. (When we come to Mendelian Laws you will see that this is a slight oversimplification of the true situation.)
When the sperm cell and an egg cell get together, a new cell is created which once again has two of each chromosome in the nucleus. This implies two alleles at each locus (or, in less technical terms, two copies of each gene, one derived from the mother and one from the father) in the offspring. The new cell will divide repeatedly and eventually create a pigeon ready to hatch, the offspring of the two parents. Chromosomes are the bearers of the hereditary material. Many different traits are captured in one chromosome. Based on research with chickens, the following is an illustration of what might be possible. (Etches, et al, 69.) Please note: this is just an illustration, not a factually identified chromosome:
Figure 1: Traits in a chromosome.
Research showed that:
1. Only sperm and eggs link one generation to the next, hence they must carry all the information needed to produce the new individual.
2. Sperm cells are composed almost totally of nuclear material, yet they contribute as much to the next generation as does the egg with its mass of cytoplasm. Hence, the nucleus must be the location of the genetic material.
3. Chromosomes have been observed to show precise division behaviour, which is essential for the transmission of genetic information. They reside in the nucleus.
4. Both chromosomes and genes occur in pairs. (We will discuss both in more detail later.)
5. Both chromosomes and genes segregate into different cells at gametogenesis. Gametogenesis is the development and production of the male and female germ cells required to form a new individual (pigeon). (Http://www.MedicineNet.com.)
Chormosome segregation appears to be independent,
meeting the requirements of Mendel’s
Taken together, these facts prove that chromosomes are the location of genetic information.
Armed with this knowledge, we are now better able to understand and follow the events which occur during processes involving cells. To reiterate: The starting point for an organism is a female cell, the ovum, fertilized by a male cell, the spermatozoon. The fertilized ovum divides into two daughter-cells, then into four, and so on until another pigeon has been created. Before a cell gives rise to the two daughter-cells, each chromosome divides into two equal parts; this is accompanied by the splitting of each gene pair. This basic process occurs with every cell division, which is the reason we find the eighty typical chromosomes in every cell of the pigeon’s body.
There is, however, one exception. When the sexual cells are formed, something special takes place just before sexual maturity (i.e. just before the sexual organs become functional); the “primitive cells” or “mother-cells” (the cells which are to manufacture the spermatozoa or ova) will be subject to a special kind of cell division known as meiosis or reductional division. In this process the two chromosomes of each pair will separate and move apart (without splitting) with the consequence that each mother-cell will give rise to two “spermatozoon” or two “ovum” cells, each containing only half the normal number of chromosomes. For the pigeon, forty single chromosomes in place of the forty chromosome pairs of the other cells of the body; in the sexual cells the genes are similarly reduced.
When a spermatozoon from the father fuses with the ovum from the mother, as happens at the time of fertilisation, each partner provides its forty chromosomes; the male and female, therefore, each play an identical role. The fertilized ovum consequently has 40 x 2 chromosomes, which will be able to pair up. It is therefore clear that reductional division is an essential process which prevents each new generation from seeing the number of its chromosomes double. The process of genetic development can be illustrated as follows:
Figure 2: The process of genetic development.
If two homologous genes (one paternal and one maternal) are completely identical, we speak of a pair of homozygotic genes; in the converse case we say that the genes are heterozygotic. In the latter event, one gene is most frequently dominant over the other, which is said to be recessive. This is important and we will discuss the implications of this when we come to the Mendelian Laws.
I am giving the list of references with this first article only. Repeating it with every article will take up too much space. I will, however, list any new references that I might consult in future.
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Chalmers, Gordon A., April 2004. Pattern
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Oltenacu, E.A., van Vleck, 1987. Genetics for the animal Sciences.
W. H. Freeman and Company,
De Scheemaker, Noël. Date unknown. The fancier’s “knack”
shapes the quality of a breed. Natural
Etches, R.J.; Verrinder Gibbens, A.M. 1993. Manipulation of the Avian Genome. CRC Press,
Hill, R. The 11th Fight myth exploded and now, the 12 fighters. SA Racing Pigeon. April-May – June 1991. No 4, Vol 5.
http://bowlingsite.mef.com/Genetics/BasGen4.html. The relationship of genes to traits (single locus).
http://bowlingsite.mef.com/Genetics/Bas Gen.html. Size as an example of additive inheritance.
http://bowlingsite.mcf.com/Genetics/Inbreeding.html. Inbreeding and Linebreeding.
http://cellbio.utmb.edu/cellbio/nucleus2.htm. A Microscopist’s View of Chromosome Organization.
http://members.aol.com/IzatKK.size.html. Breeding for Proper Size.
http://members.aol.com/malndobe/inbreed.htm. Inbreeding Coefficient.
http://oak.cats.ohiou.edu/~jm703496/es-ssbrd.html. Sexual Selection in Birds.
http://plato.stanford.edu/entries/genotype-phenotype/ The Genotype/Phenotype Distinction.
http://users.senet.com.au/~petero/geneticbreeding.htm. Breeding from a Genetic Viewpoint.
http://www.angelfire.com/oh/raraavis/genetics.html. Tom’s Genetic Page.
http://www.animal.ufl.edu/ans3384/Role-Genetics.htm. The Role of Genetics in the Horse
http://www.cabinsoftware.biz/Genetics_Tutorial/Part 2 - 13.htm. Avian Genetics.
http://www.compusmart.ab.ca/kbush/complexinheritance.htm. Complex Inheritance.
http://www.hyperdictionary.com/dictionary/nucleotide. Meaning of nucleotide.
http://www.infomatrix.jax.org/silver/9.5shtml. Quantitative Traits and Polygenic Analysis.
http://www.jasn.org/cgi/content/full/11/suppl_2/S101. Effect of Genetic Background on the Phenotype of Mouse Mutations.
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Van Breemen, Steven. 1993. The Art of Breeding. The “Paperwork” Breeding Technique. Racing Pigeon Pictorial. Number 277. Volume 24.
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Van Breemen, Steven. 1999. What can inbreeding teach us?
Winning Internet Magazine.
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