RESUMEN
It is crucial to lower the domain spacing in the application of directed self-assembly (DSA) of block copolymers. Architectural design of block copolymers provides a possible route. However, the change of the segregation degree is always coupled with that of domain spacing. Therefore, we rescale the segregation degrees of different multiblock copolymers with reference to that of the AB diblock using self-consistent field theory (SCFT), including the [AB]n linear multiblock, AnBn multi-arm star and Ad,nBd,n dendron-like, such that the density profiles of the lamellar morphology are consistent. Then we compare the lamellar periods of these different copolymers under the condition of equivalent segregation degrees. We find that the star and dendron-like architectures can significantly lower the domain spacing relative to that of the AB diblock, especially when the arm number or the generation number is large. On one hand, our work presents a simple criterion for quantifying the reduction of domain spacing of a specific multiblock architecture relative to that of the AB diblock. On the other hand, our conclusion provides a useful guide for the application of directed self-assembly.
RESUMEN
Chromosomal inversions can provide windows onto the cytogenetic, molecular, evolutionary and demographic histories of a species. Here we investigate a paracentric 1.17-Mb inversion on chromosome 4 of Arabidopsis thaliana with nucleotide precision of its borders. The inversion is created by Vandal transposon activity, splitting an F-box and relocating a pericentric heterochromatin segment in juxtaposition with euchromatin without affecting the epigenetic landscape. Examination of the RegMap panel and the 1001 Arabidopsis genomes revealed more than 170 inversion accessions in Europe and North America. The SNP patterns revealed historical recombinations from which we infer diverse haplotype patterns, ancient introgression events and phylogenetic relationships. We find a robust association between the inversion and fecundity under drought. We also find linkage disequilibrium between the inverted region and the early flowering Col-FRIGIDA allele. Finally, SNP analysis elucidates the origin of the inversion to South-Eastern Europe approximately 5000 years ago and the FRI-Col allele to North-West Europe, and reveals the spreading of a single haplotype to North America during the 17th to 19th century. The 'American haplotype' was identified from several European localities, potentially due to return migration.
