Art and Science in Breeding: Creating Better Chickens

Art and science marry in Ethiopia's quest for the perfect chicken

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The first breeds of chickens can be observed on paintings and drawings of the Renaissance in the 16th century, although earlier inbreeding is most probable. It is only later in the middle of the 19th century that there is a real explosion of creation of breeds accompanied by detailed phenotypic descriptions of these breeds in so-called Standards. All this resulted in more than thousand breeds all over the world, some specifically selected for egg production layers or meat broilers. At the end of the 19th century and throughout the 20th century, the agricultural revolution resulted in extreme selection for economic breeds of layers and broilers.

It is thus not surprising that poultry became the second largest source of meat worldwide and is forecast to surpass pork by Fig. The global meat market for chicken has surpassed that for beef at the beginning of the century and is expected to surpass pork in the next few years. In each generation information is passed from parents to offspring. The genome refers to the entire hereditary information of an organism.

In higher organisms, such as men and chicken, this information is stored in one set of molecules, collectively called the DNA, that is present in the nucleus of each cell.

A single DNA molecule represents one chromosome and is a double stranded linear molecule that contains genes. The human genome contains 23 pairs of chromosomes. For each pair, one chromosome is inherited from the father and the other from the mother. Genes consist of coding exons and non-coding introns regions, and code for proteins, which have a function in the cell and are responsible for normal functioning of the organism.

New advanced poultry facility combines art and science to boost nutrition and incomes in Ethiopia

As an organism grows, in each somatic cell division, called mitosis, the two DNA strands are separated and duplicated to yield two progeny cells with an identical amount of DNA as the progenitor cell. As such each somatic cell in the body contains an identical number of chromosomes.

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This is called the diploid number 2n since all chromosomes appear in homologous pairs in somatic cells. In the meiosis, two gametes sperm cells or egg cells are produced that each have half of the genetic information of the progenitor cell. Each gamete receives one chromosome of each homologous chromosome pair and is haploid n. The building blocks of DNA, the nucleotides, contain three essential components: There are four different nucleotides in DNA each differing in the base: The two DNA strands are bound by hydrogen bonds between the bases of the nucleotides.

The bases are complementary: A is always coupled to T, and C to G. The sequence of these nucleotides encodes the information.

A gene exists of coding regions or exons interspersed by non-coding regions or introns. The genetic code is a triplet and therefore each sequence of three nucleotides encodes for one of the 20 possible amino acids that are the chemical building blocks of proteins. Mutations cause changes in the nucleotide sequence of the DNA leading to different forms of genes called alleles. This genetic variation can result in variations in protein structures or in protein concentrations and as such change a characteristic of the organism, referred to as its phenotype.

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An individual organism has two copies of each gene. If these two copies are identical alleles, the individual is homozygous for this gene. If the two copies are different alleles it is heterozygous. One type of mutation that is very abundant in the genome is a single nucleotide polymorphism SNP which occurs when one nucleotide A, C, G or T differs between individuals of a species or between paired chromosomes in an individual.

As SNP are that abundant and fairly easy to determine, they are very important in genetic analysis. However, in order to perform a high quality genetically analysis, a large number typically sixty thousand to several million of SNP have to be determined. For this, SNP chips were developed. They are a very powerful tool in genetic analysis. In this study a 60, SNP chip specific for the chicken genome was used. While one gene codes for one protein, these proteins usually interact producing very complex phenotypes.

For example the single comb, pea comb, rose comb and walnut comb in chicken are four different phenotypes caused by the interaction of two different genes. In many organisms, sex of the individual is genetically determined by the presence or absence of particular sex chromosomes. If the sex chromosomes are the same this is called the homogametic sex and in all mammals, including men, this is the female XX while the heterogametic sex is the male XY.

In chickens this is the opposite: The sex chromosomes in chickens are referred to as Z and W to make a clear distinction with the X and Y of mammals. Inbreeding is defined as the mating of relatives. The inbreeding coefficient is a measure of the degree at which pairs of alleles on randomly chosen loci in an individual are identical homozygous by descent.

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Because an individual inherits one allele from the father and one allele from the mother, this identity by descent can only occur if both parents have a common ancestor. Inbreeding leads to a higher degree of homozygosity and is commonly used to create breeds with the purpose to make the animals homozygous for the alleles underlying desired traits. It results in more uniform populations with fixed characteristics but with less genetic diversity.

If the level of inbreeding in a certain population is very high some disadvantages will occur, called inbreeding depression. Since all individuals are more alike, the genetic diversity is decreased which results in an impaired ability to adapt to a changed environment. Moreover genetic defects may occur and survival rate and fertility may be hampered.

In case of crossing different inbred strains there is a good chance that the two parent populations are homozygous for different alleles, resulting in a higher degree of heterozygosity in the crossbreeds. This will have a positive effect on the survival rate and fertility of the crossbred animals. Moreover the genetic diversity in the crossbred population will be higher resulting in a better ability to adapt to a changing environment.

Usually crossbred animals perform better than expected from the mid-parent. This is called hybrid vigour. Chicken and human shared a common ancestor approximately million years ago, evolving into the lineages that gave rise to dinosaurs, birds and reptiles on one hand and mammals on the other. During this evolution, average genome size in birds has dropped in comparison to that in mammals: This difference in size is largely due to a much lower content of repetitive elements in the chicken genome Zhang et al.

Apart from the lower repeat content, the smaller genome is also a consequence of the fact that the chicken genome harbours consistently less genes and the genes are on average significantly shorter than their human counterparts, mainly due to smaller introns and reduced intergenic distances that resulted in an increased gene density Zhang et al.

Birds not only differ from mammals in overall genome size however, but they are also characterized by a wide variability in chromosome sizes. A distinction is made between macro chromosomes MACs and micro chromosomes MICs , although the assignment of chromosomes to either group is not consistent between different research groups: The International Chicken Genome Sequencing Consortium designated chicken chromosomes 1 through 5 and Z to the MAC group, chromosomes 6 through 10 to the intermediate size chromosomes group and the rest to the MIC group.

In contrast, other research groups designate chromosomes 1 through 8 as well as the sex chromosomes W and Z to the MAC group and all the other chromosomes to the MIC group. Because of their small size, it is even still unclear exactly how many micro chromosomes the chicken genome contains. Although theories exist to explain the existence of micro chromosomes in birds and reptiles, it is largely unknown how evolution has led to these small chromosomes.

Another distinctive difference between macro- and micro chromosomes is gene density. Analyses of the whole genome sequence have indicated that a chicken has between 20, and 23, genes. Briefly, starting from the crossbreed of two purebred chickens Mechelse Koekoek x Poule de Bresse , every generation is then crossed with a few animals from another breed. The setup is shown schematically in Figure 3.

Experimental setup of the CCRP, depicting the sequence of pure chicken lines that were subsequently crossed into the subsequent hybrids. The experimental population consisted of purebred animals, crossbreds and Red, Green, Yellow and Grey Jungle fowl Red: In this experiment however, only the genotypes of 13 purebred and 13 crossbred populations were used Fig. All animals were kindly provided by Koen Vanmechelen and several hobby breeders. Of each animal, feathers, muscle or blood were collected for DNA extraction. Each animal was photographed.

Ancestry of individual animals was not available. The latter precludes traditional approaches such as linkage analysis. The genotyping of the samples was performed with the commercially available Illumina chicken 60k SNP chip Groenen et al. The SNP chip contained approximately 58, SNPs and SNPs were equally divided across the genome, taking into consideration that recombinations are in general more frequent on the micro chromosomes. For every breed or crossbred it was studied how many SNPs had 2 alleles segregating in the population.

Those two alleles could occur within one individual when it is heterozygous or between two individuals when both are homozygous for one of the two alleles. When crossing two breeds the total number of expected informative SNPs is at least equal to the maximum number if there is a complete overlap but probably more because in both breeds different SNPs are informative.

The number of effective informative SNPs is the number found in this specific population and is probably less than the expected number because heterozygosity is lost due to random sampling of sometimes a small number drift. Informative SNPs typically segregate within a given population and therefore they are a good indication for genetic diversity within a population.

Ethiopia in bid to create SUPER CHICKENS using ALL breeds in the world

The number of expected informative SNPs can be defined as an estimation of the number of informative SNP in a generation given that the population is of sufficient size to maintain all informative SNPs. However, as the set-up of the CCP was to generate new generations by crossing the former generation with a limited number of pure bred cocks or hens of a new, purebred population, the condition of sufficient population size cannot be met. Results are indicated in Table I and Figure 4. Mechelse English Redcap, 4.

Mechelse Jersey Giant, 5. Mechelse Dresdner Hunh, 6. Mechelse Thai Fighter, 9. Mechelse Denzili Longcrower, Expected informative SNPs show a steady increase in number over the consecutive generations Fig. This number however dramatically increases when crossing Mechelse Koekoek with Poule de Bresse. The cross product of both pure lines, the Mechelse Bresse generation 2 , has expected informative SNPs, which is an increase of informative SNPs.

From then on, in the following generations, increase in expected informative SNPs ranges from with an average of per generation Table 1, Fig. The dramatic increase in genetic diversity in generation 2 compared to generation 1 can be explained by the fact that two heavily inbred lines with very different phenotypic characteristics Mechelse Koekoek and Poule de Bresse were crossed.

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As mentioned before, inbreeding leads to a higher degree of homozygosity and is commonly used to create breeds with the purpose to make the animals homozygous for the alleles underlying desired traits. In case different inbred lines or breeds are crossed, chances are high that the two parent populations are homozygous for different alleles, resulting in a much higher degree of heterozygosity in the crossbreeds. As until now, the effect of crossing on the genetic diversity of chickens is relatively unknown, this is an important result that generates important insights. Furthermore, when the results in the chicken genome are extrapolated to the human genome, increasing migration and exchange of genetic material could progressively give rise to a cosmopolitan genome of the human population as well.

However, important to keep in mind is that these results imply that, both in chicken and men, populations that admix are sufficiently large to maintain all informative SNPs from previous generations. When, like in the Cosmopolitan Chicken Project, small generations are crossed with one male or female of another, purebred population, results are completely different. With new research demonstrating that just one egg a day can prevent stunting and enhance the brain development of young children, the poultry facility is a great opportunity to improve nutrition in Ethiopia.

Part of the work at Incubated Worlds will involve bringing in farmer associations to study more efficient breeding practices and to learn about the latest improvements in feeding and raising chickens to help them develop and grow viable poultry businesses. Meron Mulatu , communications and publishing officer E-mail: Petra Remans , community manager E-mail: His work explores the importance of biocultural diversity, identity and community. His wide-ranging creative practice marries exceptional artistry, technological experimentation and scientific research.

He is best known for his ongoing Cosmopolitan Chicken Project CCP , which he first launched in to explore cultural and biological diversity. A crossbreeding program—through which the artist breeds chickens from around the world—CCP fosters a dialogue on national identity and the interdependence of different cultures, species and the environment. CGIAR is a global research partnership for a food-secure future. CGIAR science is dedicated to reducing poverty, enhancing food and nutrition security and improving natural resources and ecosystem services.

Its research is carried out by 15 CGIAR centres in close collaboration with hundreds of partners, including national and regional research institutes, civil society organizations, academia, development organizations and the private sector. You are commenting using your WordPress.

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