So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Summary
1Measurements of phytohemagglutinin (PHA)-induced tissue swelling are arguably the most popular surrogates for immunocompetence in wild birds. It is largely unresolved, however, whether the basic assumption underlying these measures is valid, particularly whether more swelling represents a ‘better’ or ‘stronger’ cell-mediated immune response.
2In this study we took a first step towards such validation by characterizing immune cell infiltration over time into the wing-webs (patagia) of PHA-challenged House Sparrows (Passer domesticus). Relative to saline-injected wing-webs, PHA-injected wing-webs displayed intensive infiltration of many immune cell types, including basophils, eosinophils, heterophils, lymphocytes, macrophages and thrombocytes. The abundance of most of these cell types changed over the course of the swelling response (6–48 h post-injection). Peak infiltration time varied depending on cell type. At several time points, significant correlations between the numbers of some cell types (particularly heterophils) and the degree of swelling were detected.
3Together, these data indicate that PHA-induced swelling is related to heightened immune cell activity in House Sparrows, but also that the PHA swelling response in this species is dynamic and involves both innate and adaptive components of the immune system. We thus caution against interpreting larger swellings as ‘greater cell-mediated immunocompetence’, given the complex nature of this immune response.

Phytohemagglutinin-induced skin swelling in birds : histological support for a classic immunoecological technique

Nutritional modulation of immune function in broilers.

Genetic Analysis of Immunocompetence Measures in a White Leghorn Chicken Line

The major histocompatibility complex (MHC) is present within the genomes of all jawed vertebrates. MHC genes are especially important in regulating immune responses, but even after over 80 years of research on the MHC, much remains to be learned about how it influences adaptive and innate immune responses. In most species, the MHC is highly polymorphic and polygenic. Strong and highly reproducible associations are established for chicken MHC-B haplotypes in a number of infectious diseases. Here, we report (1) the development of a high-density SNP (single nucleotide polymorphism) panel for MHC-B typing that encompasses a 209,296 bp region in which 45 MHC-B genes are located, (2) how this panel was used to define chicken MHC-B haplotypes within a large number of lines/breeds and (3) the detection of recombinants which contributes to the observed diversity. A SNP panel was developed for the MHC-B region between the BG2 and CD1A1 genes. To construct this panel, each SNP was tested in end-point read assays on more than 7500 DNA samples obtained from inbred and commercially used egg-layer lines that carry known and novel MHC-B haplotypes. One hundred and one SNPs were selected for the panel. Additional breeds and experimentally-derived lines, including lines that carry MHC-B recombinant haplotypes, were then genotyped. MHC-B haplotypes based on SNP genotyping were consistent with the MHC-B haplotypes that were assigned previously in experimental lines that carry B2, B5, B12, B13, B15, B19, B21, and B24 haplotypes. SNP genotyping resulted in the identification of 122 MHC-B haplotypes including a number of recombinant haplotypes, which indicate that crossing-over events at multiple locations within the region lead to the production of new MHC-B haplotypes. Furthermore, evidence of gene duplication and deletion was found. The chicken MHC-B region is highly polymorphic across the surveyed 209-kb region that contains 45 genes. Our results expand the number of identified haplotypes and provide insights into the contribution of recombination events to MHC-B diversity including the identification of recombination hotspots and an estimation of recombination frequency.

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A high-density SNP panel reveals extensive diversity, frequent recombination and multiple recombination hotspots within the chicken major histocompatibility complex B region between BG2 and CD1A1.

B-complex associated immunity to Salmonella enteritidis challenge in congenic chickens

An examination of the utility of heterophil-lymphocyte ratios in assessing stress of caged hens

The influence of the major histocompatibility (B) complex and sex on the phytohaemagglutinin (PHA) wattle response was studied in 136 segregants (B2/B2, B2/B5 and B5/B5) of a fourth generation cross between inbred lines 6(1) and 15(1) At 6 weeks of age, chickens were injected with 100 micrograms purified PHA-P Wattle thickness measurements were taken 4, 24, 48, 72 and 96 h after injection Analysis of variance showed that 4 h after injection, males had a significantly higher response than females but the sex-genotype interaction was also significant Females had higher responses than males 24 and 48 h after injection as a consequence of more rapid development and earlier resolution of the reaction in males B2/B2 chickens had significantly lower responses than B5/B5 chickens 72 and 96 h after injection, signifying a faster late resolution phase in the B2/B2 genotype The developmental and early resolution phases of the PHA wattle response were influenced by sex while the late resolution phase was influenced by B genotype

Paul F. Cotter

Papers

B-complex associated immunity to Salmonella enteritidis challenge in congenic chickens

An examination of the utility of heterophil-lymphocyte ratios in assessing stress of caged hens

Major histocompatibility (B) complex and sex effects on the phytohaemagglutinin wattle response.

Major Histocompatibility (B) Complex-Associated Differences in the Delayed Wattle Reaction to Staphylococcal Antigen

Directional selection for specific sheep cell antibody responses affects natural rabbit agglutinins of chickens