The evolution of selfing in Arabidopsis thaliana

Unlike most of its close relatives, Arabidopsis thaliana is capable of self-pollination. In other members of the mustard family, outcrossing is ensured by the complex self-incompatibility (S) locus,which harbors multiple diverged specificity haplotypes that effectively prevent selfing. We investigated the role of the S locus in the evolution of and transition to selfing in A. thaliana. We found that the S locus of A. thaliana harbored considerable diversity, which is an apparent remnant of polymorphism in the outcrossing ancestor. Thus, the fixation of a single inactivated S-locus allele cannot have been a key step in the transition to selfing. An analysis of the genome-wide pattern of linkage disequilibrium suggests that selfing most likely evolved roughly a million years ago or more.     

A molecular basis for natural selection at the timeless locus in Drosophila melanogaster

Diapause is a protective response to unfavorable environments that results in a suspension of insect development and is most often associated with the onset of winter. The ls-tim mutation in the Drosophila melanogaster clock gene timeless has spread in Europe over the past 10,000 years, possibly because it enhances diapause. We show that the mutant allele attenuates the photosensitivity of the circadian clock and causes decreased dimerization of the mutant TIMELESS protein isoform to CRYPTOCHROME, the circadian photoreceptor. This interaction results in a more stable TIMELESS product. These findings reveal a molecular link between diapause and circadian photoreception.     

杜鹃花杂交、自交及开放授粉结实性研究

选用'小叶铁红'、'玉麒麟'、'红珍珠'、'红粉玉蝶'、'粉金蝶'、'火花'6个杜鹃花品种为母本,'映山红'、'满山红'、'羊踯躅'、'大白花'4个野生资源为父本,进行6×4不完全双列杂交,并通过部分反交、自交和开放授粉,对其结实性进行了探讨.结果表明:(1)不同品种与种间杂交结实率存在明显差异,各杂交组合的结实率为0～94.0%;(2)同一品种(种)作父本或母本,其杂交结实率也有明显差异,因此,在人工杂交过程,除选择好亲本外,还要注意确定正反交组合的数量;(3)不同品种(种)自交和天然授粉结实率存在明显差异,自交结实率为12.3%～76.1%,天然授粉结实率为0～21.7%.雄蕊完全瓣化或花药败育者天然授粉结实率为零.     

两个玉米群体的构建及其改良效果

[目的]通过群体的创建和改良,扩大玉米种质基础,为广西玉米杂交育种提供新的优良种质.[方法]根据配合力测定和自交系的系谱分析结果和育种目标要求,分别应用37、26个优良自交系创建两个玉米基础群体GZPA和GZPB,应用经简化后的改良HS相互轮回选择法对两个群体进行遗传改良,并对其农艺性状进行测定和遗传增益分析.[结果]经改良后,两群体杂交组合4个试点的平均产量增益为7.70%,其吐丝天数、开花间隙天数、穗长、穗粗、穗行数、行粒数、出籽率、千粒重均获得一定程度的有利增益.GZPA和GZPB平均产量增益分别为5.37%和4.85%;群体GZPA的吐丝天数、开花间隙天数、出籽率为负增益,其他性状为正增益,且株高、穗粗、穗行数的增益达显著水平;群体GZPB的吐丝天数、开花间隙天数、穗长、穗粗、穗行数、行粒数为正增益,其他性状为负增益.两个群体改良前后性状变异系数变化较小.[结论]简化后的改良HS相互轮回选择法对两个群体的改良效果明显,两个群体内仍有较大的遗传变异,可作进一步改良.     

Evidence for a one-allele assortative mating locus

Theoretical models have shown that speciation with gene flow can occur readily via a "one-allele mechanism," where the spread of the same allele within both of two diverging species reduces their subsequent hybridization. Here we present direct genetic evidence for such an allele in Drosophila pseudoobscura. Alleles conferring high or low assortative mating in D. pseudoobscura produce the same effects when inserted into D. persimilis. This observation suggests that the type of genetic variation that is most conducive to controversial modes of speciation with gene flow, such as reinforcement or sympatric speciation, is present in nature.     

Study on the selection of a new chestnut variety-

通过选优和对比分析,选育出了板栗新品种“豫栗王”．经与“信阳大板栗”和“豫罗红”对比试验,结果表明,“豫栗王”具有丰产性强、品质优良、抗病虫等明显的优良性状,是豫南地区值得大面积推广的优良品种．     

六个荷花品种杂交、自交和开放授粉结实性研究

选用‘晨光’、‘友谊牡丹莲’、‘瑰丽’、‘红樱桃’、‘厦门碗莲’和‘素馨’6个荷花品种进行不完全双列杂交,并通过自交和开放授粉,对其结实性进行了探讨。结果表明：（1）不同品种间杂交结实率存在明显差异,各杂交组合的结实率为0～38．77％。（2）同一品种作父本或母本,其杂交结实率也有明显差异。因此,在人工杂交过程,除选择好亲本外,还要注意正反交组合。（3）不同品种自交和天然授粉结实率存在明显差异,自交结实率为0．91％-25．39％;天然授粉结实率为1．45％-54．55％,重瓣性品种自交和天然授粉结实率低。     

Darwinian evolution can follow only very few mutational paths to fitter proteins

Five point mutations in a particular beta-lactamase allele jointly increase bacterial resistance to a clinically important antibiotic by a factor of approximately 100,000. In principle, evolution to this high-resistance beta-lactamase might follow any of the 120 mutational trajectories linking these alleles. However, we demonstrate that 102 trajectories are inaccessible to Darwinian selection and that many of the remaining trajectories have negligible probabilities of realization, because four of these five mutations fail to increase drug resistance in some combinations. Pervasive biophysical pleiotropy within the beta-lactamase seems to be responsible, and because such pleiotropy appears to be a general property of missense mutations, we conclude that much protein evolution will be similarly constrained. This implies that the protein tape of life may be largely reproducible and even predictable.     

Natural selection on a major armor gene in threespine stickleback

Experimental estimates of the effects of selection on genes determining adaptive traits add to our understanding of the mechanisms of evolution. We measured selection on genotypes of the Ectodysplasin locus, which underlie differences in lateral plates in threespine stickleback fish. A derived allele (low) causing reduced plate number has been fixed repeatedly after marine stickleback colonized freshwater from the sea, where the ancestral allele (complete) predominates. We transplanted marine sticklebacks carrying both alleles to freshwater ponds and tracked genotype frequencies over a generation. The low allele increased in frequency once lateral plates developed, most likely via a growth advantage. Opposing selection at the larval stage and changing dominance for fitness throughout life suggest either that the gene affects additional traits undergoing selection or that linked loci also are affecting fitness.     

Evolutionarily assembled cis-regulatory module at a human ciliopathy locus

Neighboring genes are often coordinately expressed within cis-regulatory modules, but evidence that nonparalogous genes share functions in mammals is lacking. Here, we report that mutation of either TMEM138 or TMEM216 causes a phenotypically indistinguishable human ciliopathy, Joubert syndrome. Despite a lack of sequence homology, the genes are aligned in a head-to-tail configuration and joined by chromosomal rearrangement at the amphibian-to-reptile evolutionary transition. Expression of the two genes is mediated by a conserved regulatory element in the noncoding intergenic region. Coordinated expression is important for their interdependent cellular role in vesicular transport to primary cilia. Hence, during vertebrate evolution of genes involved in ciliogenesis, nonparalogous genes were arranged to a functional gene cluster with shared regulatory elements.     

Characterization of a common susceptibility locus for asthma-related traits

Susceptibility to asthma depends on variation at an unknown number of genetic loci. To identify susceptibility genes on chromosome 7p, we adopted a hierarchical genotyping design, leading to the identification of a 133-kilobase risk-conferring segment containing two genes. One of these coded for an orphan G protein-coupled receptor named GPRA (G protein-coupled receptor for asthma susceptibility), which showed distinct distribution of protein isoforms between bronchial biopsies from healthy and asthmatic individuals. In three cohorts from Finland and Canada, single nucleotide polymorphism-tagged haplotypes associated with high serum immunoglobulin E or asthma. The murine ortholog of GPRA was up-regulated in a mouse model of ovalbumin-induced inflammation. Together, these data implicate GPRA in the pathogenesis of atopy and asthma.     

Habitat selection in a clonal plant

Rhizomatous growth may permit the nonrandom placement of ramets into different environments, but whether clonal plants are able to use this means to exercise adaptive habitat choice is not known. Western ragweed (Ambrosia psilostachya) plants are shown to preferentially colonize nonsaline soil over saline soil patches, and clones with the strongest preference for nonsaline soil are those least able to grow when restricted to saline conditions. In clonal plant species, nonrandom associations of genotypes with specific environments may thus reflect habitat selection by plants as well as selective mortality imposed by different habitat patches.     

安农0711小麦品种3B染色体茎秆强度位点鉴定

倒伏是限制小麦产量进一步提升的主要因素之一,而茎秆强度是衡量小麦抗倒伏性的重要指标。为了鉴定控制茎秆强度基因位点,以安农0711（较强的茎秆强度和抗倒性）和河农825（较弱的茎秆强度和抗倒性）进行杂交构建的重组自交系群体为试验材料,于2017年测定其茎秆强度,利用SSR标记将控制小麦茎秆强度的位点（Qss.ahau-3B）初步定位于3B染色体上的wmc231-barc248标记之间,物理距离约为68~162 Mb。进一步利用小麦660K SNP芯片扫描两个亲本及高低池,并基于目标区段内差异的SNP,共开发了13个CAPS标记,将控制小麦茎秆强度的位点进一步缩短在EX-6650-barc248之间（150~162 Mb）。该研究结果为后续目标位点精细定位以及候选基因克隆提供了重要理论依据。     

No major schizophrenia locus detected on chromosome 1q in a large multicenter sample

Reports of substantial evidence for genetic linkage of schizophrenia to chromosome 1q were evaluated by genotyping 16 DNA markers across 107 centimorgans of this chromosome in a multicenter sample of 779 informative schizophrenia pedigrees. No significant evidence was observed for such linkage, nor for heterogeneity in allele sharing among the eight individual samples. Separate analyses of European-origin families, recessive models of inheritance, and families with larger numbers of affected cases also failed to produce significant evidence for linkage. If schizophrenia susceptibility genes are present on chromosome 1q, their population-wide genetic effects are likely to be small.     

Susceptibility locus for Alzheimer's disease on chromosome 10

The apolipoprotein E (APOE) gene is the only genetic risk factor that has so far been linked to risk for late-onset Alzheimer's disease (LOAD). However, 50 percent of Alzheimer's disease cases do not carry an APOE4 allele, suggesting that other risk factors must exist. We performed a two-stage genome-wide screen in sibling pairs with LOAD to detect other susceptibility loci. Here we report evidence for an Alzheimer's disease locus on chromosome 10. Our stage one multipoint lod score (logarithm of the odds ratio for linkage/no linkage) of 2.48 (266 sibling pairs) increased to 3.83 in stage 2 (429 sibling pairs) close to D10S1225 (79 centimorgans). This locus modifies risk for Alzheimer's disease independent of APOE genotype.