Selective sweeps of variation caused by fixation of major genes may have a dramatic impact on the genetic gain from background polygenic variation, particularly in the genome regions closely linked to the major gene. The response to selection can be restrained because of the reduced selection intensity and the reduced effective population size caused by the increase in frequency of the major gene. In the context of a selected population where fixation of a known major gene is desired, the question arises as to which is the optimal path of increase in frequency of the gene so that the selective sweep of variation resulting from its fixation is minimized. Using basic theoretical arguments we propose a frequency path that maximizes simultaneously the effective population size applicable to the selected background and the selection intensity on the polygenic variation by minimizing the average squared selection intensity on the major gene over generations up to a given fixation time. We also propose the use of mating between carriers and non-carriers of the major gene, in order to promote the effective recombination between the major gene and its linked polygenic background. Using a locus-based computer simulation assuming different degrees of linkage, we show that the path proposed is more effective than a similar path recently published, and that the combination of the selection and mating methods provides an efficient way to palliate the negative effects of a selective sweep.
Tea (Camellia sinensis) has a long history of medicinal use in the world. The chemical components of tea mainly consist of polyphenols (TPP), proteins, polysaccharides (TPS), chlorophyll, alkaloids, and so on. Great advances have been made in chemical and bioactive studies of catechins and TPP from tea in recent decades. However, the TPS from tea materials have received much less consideration than that of TPP. The number of relevant publications on the TPS from tea leaves and flowers has increased rapidly in recent years. This mini-review summarizes the structure-function relationship of TPS from tea leaves and flowers. The application of purified TPS from tea material as functional or nutritional foods was still little. It will help to develop the function foods with tea TPS and better understand the structure-bioactivity relationship of tea TPS.
Parallel speciation can occur when traits determining reproductive isolation evolve independently in different populations that experience a similar range of environments. However, a common problem in studies of parallel evolution is to distinguish this hypothesis from an alternative one in which different ecotypes arose only once in allopatry and now share a sympatric scenario with substantial gene flow between them. Here we show that the combination of a phylogenetic approach with life-history data is able to disentangle both hypotheses in the case of the intertidal marine snail Littorina saxatilis on the rocky shores of Galicia in northwestern Spain. In this system, numerous phenotypic and genetic differences have evolved between two sympatric ecotypes spanning a sharp ecological gradient, and as aside effect of the former have produced partial reproductive isolation. A mitochondrial phylogeny of these populations strongly suggests that the two sympatric ecotypes have originated independently several times. Building upon earlier work demonstrating size-based assortative mating as the main contributor to reproductive isolation among ecotypes, our analysis provides strong evidence that divergent selection across a sharp ecological gradient promoted the parallel divergence of body size and shape between two sympatric ecotypes. Thus, divergent selection occurring independently in different populations has produced the marine equivalent of host races, which may represent the first step in speciation.
