The extension reached by the minimization of the polarity distances during the evolution of the genetic code

Summary The level reached by the optimization of the polarity distances during the evolution of the genetic code was investigated. The results, although not conclusive, indicate that this optimization level is higher than the data reported in the literature. The results seem compatible with the reaching of an evolutionary minimum, with respect to the optimization of the polarity distances, by the genetic code during its formation.     

Phytoecological importance,mutual redundancy and phytological threshold values of certain climatic factors

A combination of methods (intensity of indication, floristic and mesological redundancy analysis, beta-diversity analysis, principal components analysis and Wildi's interactive ranking procedure) were used to evaluate redundancy and relative phytoecological importance among 80 climatic variables in Galicia (N.W. Spain). The information they contained was found to be adequately summarized by just 3 factors thought to play a major role in regulating the distribution of the species considered in the study area and similar areas: Baudiere's QE index, mean minimum temperature in the coldest month and mean temperature range in the coldest month. For these three factors, phytoclimatic thresholds were determined by examining beta-diversity and were used to define phytoclimatic zone types.

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Resumen Se valora la redundancia e importancia fitoecológica relative de 80 variables climáticas en Galicia (N.O. de España) empleando una combinacion de diferentes metodos (intensidad indicadora, análisis de la redundancia florística y mesológica, análisis de beta-diversidad, análisis de componentes principales y el método de ordenación interactiva de Wildi). La información contenida en esta variables es adecuadamente resumida por 3 factores que juegan un papel predominante en regular la distribución de las especies consideradas en el area de estudio y areas similares: el índice QE de Baudiere, la temperatura media de las mínimas del mes más frío y la oscilación térmica del mes más frío. Para estos factores el análisis de la beta-diversidad permitió determinar los umbrales fitoclimáticos utilizados en la definición y cartografía de las zonas fitoclimáticas.

     

The effects of mating design on introgression between chromosomally divergent sunflower species

Population genetic theory suggests that mating designs employing one or more generations of sib-crossing or selfing prior to backcrossing are more effective than backcrossing alone for moving alleles across linkage groups where effective recombination rates are low (e.g., chromosomally divergent linkages). To test this hypothesis, we analyzed the effects of chromosomal structural differences and mating designs on the frequency and genomic distribution of introgressed markers using the domesticated sunflower, Helianthus annuus, and one of its wild relatives, H. petiolaris, as the experimental system. We surveyed 170 progeny, representing the end products of three different mating designs (design I, P-F₁-BC₁-BC₂-F₂-F₃; design II, P-F₁-F₂-BC₁-BC₂-F₃; and design III, P-F₁-F₂-F₃-BC₁-BC₂), for 197 parental RAPD markers of known genomic location. Comparison of observed patterns of introgression with expectations based on simulations of unrestricted introgression revealed that much of the genome was protected from introgression regardless of mating design or chromosomal structural differences. Although the simulations indicated that all markers should introgress into multiple individuals in each of the three mating designs, 20 of 58 (34%) markers from collinear linkage groups, and 112 of 139 (81%) markers from rearranged linkage groups did not introgress. In addition, the average size of introgressed fragments (12.2 cM) was less than half that predicted by theoretical models (26–33 cM). Both of these observations are consistent with strong selection against introgressed linkage blocks, particularly in chromosomally divergent linkages. Nonetheless, mating designs II and III, which employed one and two generations of sib-mating, respectively, prior to backcrossing, were significantly more effective at moving alleles across both collinear and rearranged linkages than mating design I, in which the backcross generations preceded sib-mating. Thus, breeding strategies that include sib-crossing, in combination with backcrossing, should significantly increase the effectiveness of gene transfer across complex genic or chromosomal sterility barriers.     

Optimal flower lifetimes

Summary ESS floral lifetimes satisfy the product theorem from sex allocation theory. The dimensionless time investment per flower is a symmetric function of two dimensionless gain : cost ratios, one for each gender function.     

Molecular genetic characterization of plant somatic hybrids

An efficient and easy method for genetic characterization of plant somatic hybrids is proposed. In a first qualitative approach, four somatic hybrids and their parental species (Nicotiana tabacum andN. plumbaginifolia) were characterized by DNA fingerprinting and Random Amplification of Polymorphic DNA (RAPD). After this, a quantitative estimation of the degree of parental contribution to the hybrids was carried out by means of a slot-blot analysis. Both qualitative methods, showed one hybrid identical toN. tabacum, two almost identical toN. plumbaginifolia, and a fourth similar to this parental species, but with someN. tabacum admixture. The quantitative method, for the same hybrids, gave 83%, 7%, 7%, and 37%N. tabacum DNA contribution, respectively.     

Botanical diversity in British mires

Although mires are sometimes regarded as a single, specific and even esoteric habitat-type, in their full range of development-calcareous fens to acidic bogs, lowland swamps to upland flushes, woodlands, sedgelands and mosslands-they occupy a wide range of environmental conditions and sustain a rich botanical resource. Here an outline is given of the types of mires that are widespread in Britain and their botanical resource. It is discussed with reference to some of the environmental variables and management conditions that have been shown to influence the species composition and diversity of their vegetation. Some implications that this has for the classification of mires are outlined.     

Same species,different population dynamics: Spatio-temporal differences of Undaria pinnatifida (Ochrophyta,Phaeophyceae) in the intertidal of North Patagonia,Argentina

Population dynamics can be influenced by physical and biological factors, particularly in stressful environments. Introduced species usually have great physiological plasticity, resulting in populations with different traits. Undaria pinnatifida, a macroalga originally described from northeast Asia, was introduced in Northern Patagonia, Argentina (San Matías Gulf) around 2010. To describe the spatio-temporal variability in population structure and morphometry of U. pinnatifida, we conducted monthly field samplings for 2 years at the intertidal area of two contrasting sites in the San Matías Gulf. Individuals of U. pinnatifida were classified by developmental stage, and their morpho-gravimetric variables were measured. In both intertidal sites juveniles were found in higher proportion during austral autumn and grew and matured during the autumn-winter months (from May onwards), and individuals senesced during early austral summer (December and January). Conversely, density and biomass were largely different between sites, and individuals showed slight morphological variability between sites. Environmental (e.g., nutrient concentration, available substrate) and biological factors (e.g., facilitation, competition) may explain the observed differences. Since there is not a macroalga with U. pinnatifida morphometrical characteristics in the intertidal environments of San Matías Gulf, studying this recent introduction gives us a better understanding of its potential ecological effects.     

质体在非均衡分裂下传递分配的概率

质体非均衡分裂时,其传递和分配情况复杂,重组状态多。本文分析了突变质体在各种分配情况下得到的概率,条件概率、联合概率和一细胞至少含m_0个突变质体的概率公式及计算示例。讨论了它们在生物学中的重要意义。