Much recent conservation effort has focused on genetic events in small populations, such as threatened or endangered species on the verge of extinction. However, the overwhelming causes of population reductions and extinctions worldwide are habitat destruction and the introduction of exotic species of parasites, predators, and competitors. The restoration and maintenance of healthy habitats and ecosystems should be of great concern to a mature science of conservation biology. The long-term preservation of biodiversity requires understanding not only the demography and genetics of small populations but also the ecology and evolution of abundant species. Here we show that in constant or unpredictable environments genetic variance reduces population mean fitness and increases the risk of extinction. In predictable, highly variable environments genetic variance may be essential for adaptive evolution and population persistence.Most of the characters of interest to ecologists and evolutionary biologists are quantitative characters influenced by many genes and environmental factors. Meristic and threshold characters also are amenable to analysis using quantitative genetic methods (Wright 1968, ch. 15;Falconer 1989). As examination of the fossil record attests, quantitative characters are of great importance in adaptive evolution (Simpson 1953;Carroll 1988). Although adaptive evolution can occur by mutations of large effect, the divergence in the quantitative traits that distinguish both different populations within a species and closely related species usually has a polygenic basis (Wright 1968, ch. 15;Lande 1981;Coyne 1985).No comprehensive evaluation of the importance of genetic variability in quantitative traits to population persistence and adaptation exists currently. In the short-term, genetic variability is often less critical than other determinants of population persistence (Lande 1988), but in the long-term, it can play the decisive role in allowing a population to persist and adapt in a changing environment. The rate of evolution in the mean phenotype in response to selection on a single quantitative character is proportional to the product of the additive genetic variance in the character and the intensity of directional selection (Lande 1976;Falconer 1989). However, genetic variability is thought not to be the rate-limiting factor in long-term evolution. Instead, long-term rates of evolution and adaptive radiation are constrained by ecological opportunity (Simpson 1953, pp. 77-80; Wright 1968, p. 520). That the short-and the long-term views are not inconsistent can be seen in a model of the common situation in which natural selection acting on a quantitative character (other than fitness itself) favors an intermediate phenotype. In this situation the rate of evolution in the character is limited not only by the magnitude of the additive genetic variance in the character but also by the rate of change in the optimum phenotype as the environment changes. An intermediate-optimum model such as that which follo...

We present the initial phenotypic characterization of an Arabidopsis mutation, terminal flower 1-1 (tfl1-1), that identifies a new genetic locus, TFL1. The tfl1-1 mutation causes early flowering and limits the development of the normally indeterminate inflorescence by promoting the formation of a terminal floral meristem. Inflorescence development in mutant plants often terminates with a compound floral structure consisting of the terminal flower and one or two subtending lateral flowers. The distal-most flowers frequently contain chimeric floral organs. Light microscopic examination shows no structural aberrations in the vegetative meristem or in the inflorescence meristem before the formation of floral buttresses. The wild-type appearance of lateral flowers and observations of double mutant combinations of tfl1-1 with the floral morphogenesis mutations apetala 1-1 (ap1-1), ap2-1, and agamous (ag) suggest that the tfl1-1 mutation does not affect normal floral meristems. Secondary flower formation usually associated with the ap1-1 mutation is suppressed in the terminal flower, but not in the lateral flowers, of tfl1-1 ap1-1 double mutants. Our results suggest that tfl1-1 perturbs the establishment and maintenance of the inflorescence meristem. The mutation lies on the top arm of chromosome 5 approximately 2.8 centimorgans from the restriction fragment length polymorphism marker 217.

In Arabidopsis, floral meristems arise in continuous succession directly on the flanks of the inflorescence meristem. Thus, the pathways that regulate inflorescence and floral meristem identity must operate both simultaneously and in close spatial proximity. The TERMINAL FLOWER 1 (TFL1) gene of Arabidopsis is required for normal inflorescence meristem function, and the LEAFY (LFY), APETALA 1 (AP1), and APETALA 2 (AP2) genes are required for normal floral meristem function. We present evidence that inflorescence meristem identity is promoted by TFL1 and that floral meristem identity is promoted by parallel developmental pathways, one defined by LFY and the other defined by AP1/AP2. Our analysis suggests that the acquisition of meristem identity during inflorescence development is mediated by antagonistic interactions between TFL1 and LFY and between TFL1 and AP1/AP2. Based on this study, we propose a simple model for the genetic regulation of inflorescence development in Arabidopsis. This model is discussed in relation to the proposed interactions between the inflorescence and the floral meristem identity genes and in regard to other genes that are likely to be part of the genetic hierarchy regulating the establishment and maintenance of inflorescence and floral meristems.

This study aimed to determine the increased activity of learning and learning outcomes in digestive system materials by the means of I-Spring learning medium. This research is a Classroom Action Research. The subjects were 31 students of class XI SMA Negeri 1 Enrekang South Sulawesi Province onthe second semester of academic year 2015/2016. The implementation of the action research consisted of two cycles, each cycle consisting of three meetings. The data wereobtained using observation sheet for learning activities and achievement test for learning outcomes. The data were analyzed using descriptive analysis. The results of the first cycle to the second cycle showed an increase in activity and learning outcomes. The average activity of students in the first cycle was 51.3% and the second cycle was 76.8%. The percentage of completeness student learning outcomes in the first cyclewas 70.6% and the second cycle increased to 78.5%. Based on the results of this study, it can beconcluded that the application of learning using "ISpring" medium increased the activity and students' learning outcomes for class XI SMA Negeri 1 Enrekang on thematerialofDigestive System.

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