Here we report the sequence of the region that determines rapid allograft rejection in chickens, the chicken major histocompatibility complex (MHC) This 92-kilobase region of the B locus contains only 19 genes, making the chicken MHC roughly 20-fold smaller than the human MHC Virtually all the genes have counterparts in the human MHC, defining a minimal essential set of MHC genes conserved over 200 million years of divergence between birds and mammals They are organized differently, with the class III region genes located outside the class II and class I region genes The absence of proteasome genes is unexpected and might explain unusual peptide-binding specificities of chicken class I molecules The presence of putative natural killer receptor gene(s) is unprecedented and might explain the importance of the B locus in the response to the herpes virus responsible for Marek's diseases The small size and simplicity of the chicken MHC allows co-evolution of genes as haplotypes over considerable periods of time, and makes it possible to study the striking MHC-determined pathogen-specific disease resistance at the molecular level

The chicken B locus is a minimal essential major histocompatibility complex

The past decades have seen the gradual formulation of the theory of geographical speciation, principally based on work in the fields of the systematics of mammals, birds, insects, and mollusks. This theory 'postulates that in bisexual animals a new species can develop only "if a population, which has become geographically isolated from its parental species, acquires during this period of isolation characters which prorhote or guarantee reproductive isolation when 'the external barriers break down" (Mayr, 1942). A number of workers in recent years have considered this statement an oversimplification. The omission of any reference in this description of the speciation process to the ecological factors-so vitally involved in the process of speciation-has also been objected to. Even though the importance of geographical speciation is universally admitted, there are a number of authors, particularly among the ichthyologists and entomologists, who believe that in addition to geographical speciation there is another process of speciation, variously referred to as ecological or sympatric speciation. Thorpe (1945), for example, is inclined to consider that in addition to geographical speciation there is a speciation process which is characterized by the fact "that local differences of habit may be the starting point for the evolution of new species." It appears to me that there is no real conflict between those authors who stress the ecological aspects of speciation, such as Stresemann (1943) and Thorpe (1945), and those who, like myself, have stressed the geographical aspects. This was pointed out by Timofeeff-Ressovsky (1943). The seeming differences are due partly to misunderstandings and partly to a different emphasis placed on various aspects of a single process of speciation. The field has suffered from looseness of thought and vagueness of expression, and it may therefore be ulseful to attempt a fresh analysis and possibly a synthesis of the two viewpoints. The principal obstacle blocking such synthesis up to now has been that those authors who have emphasized the role of ecological factors in speciation generally accept sympatric speciation as an integral part of ecological speciation. To remove this difficulty, a special section (pp. 269-285) has been devoted to a discussion of sympatric speciation. It is more important, however, to determine the respective roles of geographical and ecological factors in speciation, and to find out whether they operate consecutively or concomitantly. The field has suffered particularly from the lack of a clear-cut Fragestellung. The result has been that only few investigations have ever been undertaken which would give decisive answers to the unsolved questions. Most of the published studies sadly miss the crucial points. It is one additional object of this discussion to focus the attention of investigators on those aspects that are in particular need of further study.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1947.tb02723.x

Ecological factors in speciation

Lines of chickens selected from a common ancestral population for either resistance or susceptibility to Marek's disease developed contrasting frequencies of particular B alloalleles. Comparison of inoculated sibs in backcross-families revealed that the B alloalleles characterizing the two lines accounted for an eightfold difference in tumor incidence. This genetic difference in tumorigenesis associated with the alloalleles of the major histocompatibility complex is probably expressed through the cell-mediated immune system.

https://science.sciencemag.org/content/sci/195/4274/193.full.pdf

Marek's disease: effects of B histocompatibility alloalleles in resistant and susceptible chicken lines

Nutritional modulation of immune function in broilers.

Publisher Summary The chapter discusses the ontogeny and phylogeny of adaptive immunity, including the acquisition of passive and active immunity by the developing fetus in relation to the phylogenetic development of active immunologic responses and relates immunologic capacity to the function of the thymus and of the bursa of Fabricus. The development of the lymphoid system plays a key role in development of the potential for adaptive immune response. Absence of the thymus during the period of development of the peripheral lymphoid tissues results in both abnormal lymphoid development and immunologic deficiency. In phylogeny, the data suggest that the transition to adaptive immunity occurs in the lower vertebrates and that it is paralleled by the development of a lymphoid thymus, other organized lymphoid tissues, and the lymphoid system of cells. The ontogenesis of immunity is discussed in terms of the following relationships and processes : interrelationship of fetus and mother, particularly serum immunoglobulin and antibody transfer; the beginning production of immunoglobulins during fetal and neonatal life; the origins of antibody-producing capacity and ability to initiate and express delayed allergic responses; the development of capacity for homograft rejection and the decrease of susceptibility to production of tolerance in the fetal and neonatal period; and the key role of the thymus and other central lymphoid tissue in the ontogeny of the lymphoid system and adaptive immunity. The studies of the lower fishes havenot been sufficiently comprehensive particularly with the more sophisticated methods of protein chemistry that are yielding such important information concerning the nature and interrelationships of the immunoglobulins.

Ontogeny and phylogeny of adaptive immunity.

/pdf/on-multiple-alleles-effecting-cellular-antigens-in-the-knagd607mr.pdf

On multiple alleles effecting cellular antigens in the chicken.

https://www.genetics.org/content/genetics/47/10/1385.full.pdf

Transferrin Variation in Columbidae

REVIOUS studies on the blood of sheep (ANDERSEN 1938; YCAS 1949) P have shown the presence on the erythrocytes of an antigenic character, called R, demonstrable by a normally occurring antibody present in the sera of some sheep lacking the R substance. The report by YCAS suggested that the R character was inherited as a dominant in contrast to its absence. Further investigations by STORMONT (1951) showed that sheep bloods, which failed to react with anti-R reagents (i.e., typing fluids specific for the R-substance), might react with normal sera of certain cattle which had been absorbed with sheep cells of group R. This reagent obtained from cattle serum was called anti-0. In tests of over 100 sheep bloods with both anti-R and this new reagent (anti-0) , the reactions were mutually exclusive. Since the new reagent was not reactive with the cells of heterozygotes, STORMONT suggested that the genes determining the R and 0 characters were allelic, the gene for R being dominant. However, in this paper the 0 character will be called \" r \" in order to have the terminology in concordance with genetical practice. This report describes a new group \" i \" of sheep erythrocytes. Cells are classified as belonging to group i if they fail to react with both anti-R and anti-r sera. Further, this report will deal with the serological characteristics and the inheritance of the characters R, r and i.

https://www.genetics.org/content/genetics/39/3/396.full.pdf

Evidence for Epistatic Action of Genes for Antigenic Substances in Sheep.

/pdf/a-genetic-analysis-of-species-differences-in-columbidae-3yuoazu5hv.pdf

A Genetic Analysis of Species Differences in Columbidae.

OST breeds of domestic animals occupy a position in the taxonomic M hierarchy similar to that held by races in natural populations. The mechanisms leading to genetic differences in these two classes of populations are presumably much the same; the factor of human interference with the mating pattern and with selection in domestic populations is probably the only essential difference. An investigation of the genetic bases of breed differences is therefore an aspect of a problem of broad biological concernthe genetic nature of population differences within the limits of a species. Genetic studies of differences between species are limited by the difficulty, in most cases the impossibility, of obtaining viable hybrids between them, and by the frequent sterility of the hybrids even if they are obtained. For the most part, the ordinary aspects of segregation and assortment are not commonly available to the investigator of genetic similarities and differences between these reproductively isolated groups, and techniques other than hybridization must be relied upon for analyses. One productive approach has been that of immunogenetics. IRWIN and CUMLEY (1943) have shown that immunological reactions could be used to characterize the cellular antigens common to two or more species of Columba and those peculiar to particular species, i.e., not shared with others. These authors have concluded that between the two broad groups of antigens, (I) those (probably numerous) common to all species of the genus considered, and (2) those (probably few) limited to a single species, there is a third class, (3) common to certain species and absent in others. This last group of antigens exhibits a complex network of relationships among the species. Since the cellular antigens, without known exception, are gene-controlled, the immunological techniques provide a basis for a genetic analysis of species similarities and differences even when hybridization is impossible. This application is based on a t least two apparently rational assumptions: ( I ) that antigens common to two or more species are controlled by similar or identical genes, and (2) that the absence from one

https://www.genetics.org/content/genetics/32/1/64.full.pdf

An Immunogenetic Analysis of Racial Differences in Dairy Cattle.

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