Tracing origins with molecular sequences: metazoan and eukaryotic beginnings.

Milestones in the evolution of the eukaryotic cell are being discovered through the analysis of molecular sequences. As sequence data become increasingly plentiful, our ability to reconstruct the most distant evolutionary branchings of evolutionary trees is limited only by the mathematics of phylogenetic reconstruction. Analysis of ribosomal RNAs agrees with traditional analyses of morphological and developmental characters that all multicellular animals probably arose from a common ancestor, but highlights one of the major limitations of the various mathematical algorithms used. Refined methods of sequence analysis also suggest a previously unsuspected sister relationship between the eukaryotic nucleus and eocytes, a group of extremely thermophilic, sulfur-metabolizing bacteria, that questions the classical eukaryote/prokaryote division.     

The origins of molecular genetics: one gene, one enzyme

Roots presents articles on landmark discoveries that laid the basis for contemporary molecular and cellular biology. In this article, N. H. Horowitz, Professor Emeritus at the California Institute of Technology, and a former associate of George Beadle's, reviews the work that led to the one gene–one enzyme hypothesis.     

The origins of molecular genetics

Journal of the History of Biology -     

The origins of behavioral genetics

The passing of Seymour Benzer has inspired various retrospectives on his scientific career, and much attention has been paid to his inauguration of single-gene mutant studies of behavior in the fruitfly Drosophila melanogaster. Studies of genes and behavior actually go back to the beginnings of genetics. The end of the era marked by Benzer's life offers a good opportunity to look back at the origins of the field he influenced so profoundly.     

Integrating social science and genetics: news from the political front

There has been growing interest in the use of genetic models to expand the understanding of political preferences, attitudes, and behaviors. Researchers in the social sciences have begun incorporating these models and have revealed that genetic differences account for individual differences in political beliefs, behaviors, and responses to the political environment. The first Integrating Genetics and the Social Sciences Conference, held at Boulder, Colorado in May of 2010, brought together these researchers. As a result, we jointly review the last 5 years of research in this area. In doing so, we explicate the methods, findings, and limitations of behavior genetic approaches, including twin designs, association studies, and genome-wide analyses, in their application toward exploring political preferences.     

Entering the second century of maize quantitative genetics

Maize is the most widely grown cereal in the world. In addition to its role in global agriculture, it has also long served as a model organism for genetic research. Maize stands at a genetic crossroads, as it has access to all the tools available for plant genetics but exhibits a genetic architecture more similar to other outcrossing organisms than to self-pollinating crops and model plants. In this review, we summarize recent advances in maize genetics, including the development of powerful populations for genetic mapping and genome-wide association studies (GWAS), and the insights these studies yield on the mechanisms underlying complex maize traits. Most maize traits are controlled by a large number of genes, and linkage analysis of several traits implicates a ‘common gene, rare allele'' model of genetic variation where some genes have many individually rare alleles contributing. Most natural alleles exhibit small effect sizes with little-to-no detectable pleiotropy or epistasis. Additionally, many of these genes are locked away in low-recombination regions that encourage the formation of multi-gene blocks that may underlie maize''s strong heterotic effect. Domestication left strong marks on the maize genome, and some of the differences in trait architectures may be due to different selective pressures over time. Overall, maize''s advantages as a model system make it highly desirable for studying the genetics of outcrossing species, and results from it can provide insight into other such species, including humans.     

Profiles in genetics: George Wells Beadle and the origins of the gene-enzyme concept.

Beadle's success in establishing biochemical genetics on a firm foundation was due to a combination of several circumstances. These include the following: 1. Apt timing of his work, which Garrod's work clearly lacked, was important. Geneticists were receptive to his ideas and conclusions. As Beadle (1967, 1974) himself acknowledged, much ground was prepared earlier by Garrod and Haldane, who discussed gene action in terms of biochemical reactions, although it was largely ignored. The physiology of gene action was discussed and speculated on to a great extent in the preceding years by Bridges, Goldschmidt, Muller, and Wright. 2. Beadle's selection of Neurospora was most appropriate. It was a haploid organism (with no complications of dominance and recessivity) that could be grown and manipulated easily for isolating mutants to study their segregation and recombination within a short time. Its cytogenetics and the method of growing on chemically defined media were already worked out. It was devoid of the long generation time and more complex sex cycle (among other problems) that complicated the biochemical study of higher plants (e.g., Primula), which Haldane and Scott-Moncrieff had attempted earlier. 3. Beadle's striking ability to shift from one organism to another--from corn to Drosophila to Neurospora--must be acknowledged. He saw the limitations of existing methods and had the courage and skill to move on to more successful methods: from conventional breeding to tissue transplants to microbiological techniques. 4. Beadle's own curiosity about the biochemical nature of gene action and his good fortune in having had such outstanding teachers as Emerson, as well as his ability to collaborate with Ephrussi and Tatum, contributed largely to his success.     

Physiological genetics of the dominant gibberellin-nonresponsive maize dwarfs,Dwarf8 and Dwarf9

Maize (Zea mays L.) Dwarf8-1 (D8-1) is an andromonoecious dwarf mutant proposed to be involved in gibberellin (GA) reception (Fujioka et al. 1988b; Harberd and Freeling 1989). The mutant D8-1 is dominant and GA-nonresponsive (Phinney 1956). We show by map position and similarity of phenotype that five additional dwarf mutants are D8 alleles. We show by map position and similarity of phenotype that a second andromonoecious dwarf mutant, D9-1, defines a duplicate gene. Maize D9-1 and each dominant D8 allele specify a different plant stature, from very mild to very severe dwarfism. Plants of D9-1 and all dominant D8 alleles, except D8-1591, were GA-nonresponsive when treated with 7500 nmol GA₃. The behavior of the mild dwarf D8-1591 was unique in that a small but significant growth response was detected (37% for D8-1591 vs. 130% for the wild type) when treated with 7500 nmol GA₃. These results establish that all dwarf genotypes, except D8-1591, in one dose set a maximum limit on plant growth and block the normal response to GA. When treated with the GA-synthesis inhibitor paclobutrazol, plants of all dwarf genotypes and wild-type siblings were severely dwarfed. Plants of all dwarf genotypes treated with the GA-synthesis inhibitor paclobutrazol and GA₃ were returned to their normal dwarf phenotype. Dominant dwarfing, delayed flowering, increased tillering, and anther development in the ear are characteristic features of D9-1 and all D8 alleles. The GA-synthesis-deficient dwarfs also have these characteristic features. We discuss the function of the wild-type gene product in the context of the observed results.Abbreviations D8 Dwarf8 - D9 Dwarf9 - GA_(n) gibberellin A_(n) - GA₃ gibberellic acid - MNL Maize Genetics Cooperation Newsletter - NIL near-isogenic lines - RFLP restriction fragment length polymorphism - WT wild type This work was supported, in part, by a National Science Foundation Plant Postdoctoral Fellowship to R.G.W., by grants from NIH and ICI Seeds to M.F., the NSF Center for Plant Developmental Biology and the California Agriculture Experiment Station. Much of the work was done in the laboratory of Tim Helentjaris and was supported by a grant from Pioneer Hi-Bred Int'l. The generous gifts of the dominant dwarfing mutants from M.G. Neuffer and O.E. Nelson Jr. are gratefully acknowledged.     

The developmental role of serotonin: news from mouse molecular genetics

New genetic models that target the serotonin system show that transient alterations in serotonin homeostasis cause permanent changes to adult behaviour and modify the fine wiring of brain connections. These findings have revived a long-standing interest in the developmental role of serotonin. Molecular genetic approaches are now showing us that different serotonin receptors, acting at different developmental stages, modulate different developmental processes such as neurogenesis, apoptosis, axon branching and dendritogenesis. Our understanding of the specification of the serotonergic phenotype is improving. In addition, studies have revealed that serotonergic traits are dissociable, as there are populations of neurons that contain serotonin but do not synthesize it.     

Metabolite profiling of maize grain: differentiation due to genetics and environment

A comparative metabolite profiling approach based on gas chromatography-mass spectrometry (GC/MS) was applied to investigate the impact of genetic background, growing location and season on the chemical composition of maize grain. The metabolite profiling protocol involved sub-fractionation of the metabolites and allowed the assessment of about 300 distinct analytes from different chemical classes (polar to lipophilic), of which 167 could be identified. A comparison, over three consecutive growing seasons, of the metabolite profiles of four maize cultivars which differed in their maturity classification, was carried out using principal component analysis (PCA). This revealed a strong separation of one cultivar in the first growing season, which could be explained by the immaturity of the kernels of this cultivar compared with others in the field trial. Further evaluations by pair-wise comparison using Student’s t-test and analysis of variance (ANOVA) showed that the growing season was the most prominent impact factor driving variation of the metabolite pool. An increased understanding of metabolic variation was achieved by analysis of a second sample set comprising one cultivar grown for 3 years at four locations. The applied GC/MS-based metabolite profiling demonstrated the natural variation in maize grain metabolite pools resulting from the interplay of environment, season, and genotype.     

The molecular genetics of seed maturation in maize

The maturation phase of seed formation involves coordinated expression of multiple developmental pathways. These processes include abscisic acid regulated responses associated with the arrest of embryo development and induction of anthocyanin synthesis in embryo and aleurone tissues. Studies of the maturation defective vivaparous mutants of maize suggest that one gene, viviparous-1 ( vpl ), regulates both of these pathways in the developing seed. Mutations at vpl reduce the sensitivity of the developing embryo to abscisic acid. In addition, Vpl is required for expression of Cl , a regulatory gene for the anthocyanin pathway. This interaction is consistent with the idea that Vpl and Cl function as part of a regulatory hierarchy controlling seed development. Molecular studies of vpl mutations which separate control of embryo arrest and anthocyanin synthesis suggest that these functions map to discrete domains in the Vpl protein. Therefore, coordinate control of diverse maturation processes may be achieved through expression of a functionally complex regulatory molecule.     

An approach to the genetics of nitrogen use efficiency in maize

To study the genetic variability and the genetic basis of nitrogen (N) use efficiency in maize, a set of recombinant inbred lines crossed with a tester was studied at low input (N-) and high input (N+) for grain yield and its components, grain protein content, and post-anthesis nitrogen uptake and remobilization. Other physiological traits, such as nitrate content, nitrate reductase, glutamine synthetase (GS), and glutamate dehydrogenase activities were studied at the level of the lines. Genotypexnitrogen (GxN) interaction was significant for yield and explained by variation in kernel number. In N-, N-uptake, the nitrogen nutrition index, and GS activity in the vegetative stage were positively correlated with grain yield, whereas leaf senescence was negatively correlated. Whatever N-input, post-anthesis N-uptake was highly negatively related to N-remobilization. As a whole, genetic variability was expressed differently in N+ and N-. This was confirmed by the detection of QTLs. More QTLs were detected in N+ than in N- for traits of vegetative development, N-uptake, and grain yield and its components, whereas it was the reverse for grain protein content and N-utilization efficiency. Several coincidences between genes encoding for enzymes of N metabolism and QTLs for the traits studied were observed. In particular, coincidences in three chromosome regions of QTLs for yield and N-remobilization, QTLs for GS activity and a gene encoding cytosolic GS were observed. This may have a physiological meaning. The GS locus on chromosome 5 appears to be a good candidate gene which can, at least partially, explain the variation in nitrogen use efficiency.     

Telomeres: the beginnings and ends of eukaryotic chromosomes

The ends of eukaryotic chromosomes are called telomeres. This article provides a short history of telomere and telomerase research starting with the pioneering work of Muller and McClintock through the molecular era of telomere biology. These studies culminated in the 2009 Nobel Prize in Medicine. Critical findings that moved the field forward and that suggest directions for future research are emphasized.