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

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.

/pdf/heat-shock-proteins-molecular-chaperones-and-the-stress-p3ghklf1z7.pdf

Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Gel electrophoresis of proteins has become a standard and powerful research tool for application in a multitude of biological disciplines One form of protein electrophoresis, isozyme analysis, has become particularly prominent in systematic and evolutionary biology as well as agronomy (Tanksley and Orton, 1983) Isozymes, or multiple molecular forms of enzymes, are enzymes that share a common substrate but differ in electrophoretic mobility (Markert and Moller, 1959) They are revealed when tissue extracts are subjected to electrophoresis in various types of gels and subsequently submersed in solutions containing enzyme-specific stains Genetic analysis may indicate that some of the variant electromorphs are encoded by alternate alleles at a single locus, in which case the allelic products are termed allozymes (Prakash et al, 1969) Data retrieved from electrophoretic gels consist of the number and relative mobilities of various enzyme products, which with appropriate genetic analyses become transformed into single or multilocus genotypes for each individual analyzed Reasons are many for the popularity of electrophoretic data (Avise, 1975; Gottlieb, 1977; Crawford, 1983), but foremost among these is that isozymes provide a series of readily scored, single-gene markers

Visualization and Interpretation of Plant Isozymes

The female reproductive tract is where competition between the sperm of different males takes place, aided and abetted by the female herself Intense postcopulatory sexual selection fosters inter-sexual conflict and drives rapid evolutionary change to generate a startling diversity of morphological, behavioural and physiological adaptations We identify three main issues that should be resolved to advance our understanding of postcopulatory sexual selection We need to determine the genetic basis of different male fertility traits and female traits that mediate sperm selection; identify the genes or genomic regions that control these traits; and establish the coevolutionary trajectory of sexes

/pdf/postcopulatory-sexual-selection-5aiebjgt83.pdf

Postcopulatory sexual selection.

The ability to observe allelic variation at isozyme loci has revolutionized research in the fields of biochemical genetics, population genetics, and evolution. This variation, called allozymic polymorphism, has been used in plants to examine genetic processes at every stage of the life cycle and to ascertain genetic diversity in all major crops as well as many other species. Yet the potential for using allozymes as genetic markers was not immediately predicted when isozyme variability was initially described (Hunter and Marker, 1957; Markert and Moller, 1959). In fact, the extent and prevalence of allozyme polymorphism was a rather disconcerting surprise to evolutionary biologists. Classical evolutionary theory had predicted that the most “efficient” form of an enzyme should, over time, become predominant in isolated populations, with an occasional rare allele produced through mutation. The discovery in many populations of relatively high levels of polymorphism at isozyme loci has forced a major reconsideration of evolutionary theory (Kimura and Crow, 1964; Koehn et al., 1983; Kimura, 1983).

Genetics of Plant Isozymes

Biotechnology and Ecology of Pollen

Publisher Summary The angiosperm life cycle consists of two alternating phases—a diploid, morphologically elaborate and conspicuous sporophyte, and a much reduced, haploid gametophyte. At least four phenomena in the ontogeny of pollen impinge on the genetic determination of pollen quality: Cytoplasmic interconnections, which establish developmental synchrony among meiocytes, callose envelopes, which isolate microspores from each other, tapetal deposits, which coat the pollen exine, and sporophytic inputs, which remain in the meiocyte cytoplasm. Some pollen characteristics are determined exclusively by the sporophyte, as is the case with the exine. Others, such as Ga factors, gametophytic self-incompatibility, and the presence of specific enzymes (alcohol dehydrogenase, P-galactosidase, are under gametophytic control. Pollen competition may be significant phenomenon in the evolution of crop species and also in the reduction of genetic load. Pollen competition may play a significant role in the adaptive capacities of the angiosperms, as this group possesses three characteristics, which enhance pollen tube competition. These are: Heavy stigmatic loads of pollen, the simultaneous arrival of many pollen grains on the stigma, and the requirement for extensive pollen tube growth. Finally, direct and indirect in vivo interactions between pollen grains and particularly pollen-pistil interactions need evaluation.

Genetics of Angiosperm Pollen

Speed of pollen tube growth is positively correlated with the quality of the resultant sporophytic generation. Therefore, gametophytic competition may be an important adaptive mechanism. Furthermore, pollen tube growth rates may be used to predict the quality of F1crosses in crop species.

Pollen Tube Growth Rates in Zea mays: Implications for Genetic Improvement of Crops.

To determine the extent of gametophytic gene expression and the type of transcription, haploid or haplo-diploid, of the genes, isozymes were used as genetic markers. Fifteen enzymatic systems, including thirty-four isozymes, were studied. The determination of the type of expression of genes coding for multimeric enzymes was based on the comparison of electrophoretic patterns of pollen and of sporophytic tissues from plants heterozygous for electrophoretic mobility: if gene expression in pollen is of a gametophytic (haploid) origin, pollen, unlike the sporophyte, would reveal only the parental homomultimeric bands. The enzymes analyzed can be grouped in three categories according to type of gene expression: i) enzymes present in both pollen and sporophyte, coded by the same gene with haplo-diploid expression; ii) enzymes controlling analogous functions in pollen and sporophyte, coded by different genes, expressed in only one of the two phases; iii) enzymes present in two or more forms in the sporophyte and only in one form in the gametophyte. The data allow the proportion of haplo-diploid gene expression in the loci examined to be estimated at 0.72; 0.22 and 0.06 being the proportions attributable to the sporophytic and gametophytic domains, respectively.

The extent of gametophytic-sporophytic gene expression in maize.

Cellular membrane stability (CMS) is a physiological index widely used to evaluate thermostability in plants. The genetic basis of the character has been studied following two different approaches: restriction fragment length polymorphism (RFLP) analysis, and the effects of segregating heat shock protein (HSP) loci. RFLP analysis was based on a set of recombinant inbreds derived from the T32 × CM37 F1 hybrid and characterized for about 200 RFLP loci. Heritability of CMS estimated by standard quantitative analysis was 0.73. Regression analysis of CMS on RFLPs detected a minimum number of six quantitative trait loci (QTL) accounting for 53% of the genetic variability. The analysis of the matrices of correlation between RFLP loci, either within or between chromosomes, indicates that no false assignment was produced by this analysis. The effect of HSPs on the variability of the CMS was tested for a low-molecular-weight peptide (HSP-17) showing presence-absence of segregation in the B73 × Pa33 F2 population. Although the genetic variability of the character was very high (h (2)=0.58) the effect of HSP-17 was not significant, indicating either that the polypeptide is not involved in the determination of the character or that its effect is not statistically detectable.

E. Ottaviano

Papers

Biotechnology and Ecology of Pollen

Genetics of Angiosperm Pollen

Pollen Tube Growth Rates in Zea mays: Implications for Genetic Improvement of Crops.

The extent of gametophytic-sporophytic gene expression in maize.

Molecular markers (RFLPs and HSPs) for the genetic dissection of thermotolerance in maize.