Landscape heterogeneity in landform and land use provides functional resistance to gene flow in continuous Asian black bear populations.

Context: Genetic diversity is one of the most important facets of biological diversity, and changes in the spatial pattern of habitats, often modified by human activity, are believed to have affected the genetic diversity of resident natural populations.

Objectives: We undertook a landscape genetic analysis in order to determine which landscape features influence gene flow within Asian black bear populations and to identify the underlying processes.

Methods: In our evaluation of gene flow, we estimated four parameters of resistance with regard to landscape elevation: the mean, the difference between the highest and lowest, the standard deviation, and the coefficient of variation of elevation among individuals.

Validating the significance of genomic properties of Chi sites from the distribution of all octamers in Escherichia coli.

Chi sites (5'-GCTGGTGG-3') are homologous recombinational hotspot octamer sequences, which attenuate the exonuclease activity of RecBCD in Escherichia coli. They are overrepresented in the genome (1008 occurrences), preferentially located within coding regions (98%), oriented in the direction of replication (75%), and occur most commonly on the mRNA-synonymous sense strand of the double helix (79%). Previous statistical studies of the genome sequence suggested that these genomic properties of Chi sites appear to be related to their role in recombinational repair and therefore to replication and transcription.

Over-representation of Chi sequences caused by di-codon increase in Escherichia coli K-12.

Chi sequences (5'-GCTGGTGG-3') are cis-acting 8 bp sequence elements that enhance homologous recombination promoted by the RecBCD pathway in Escherichia coli. The genome of E. coli K-12 MG1655 contains 1009 Chi sequences and this frequency far exceeds the expected value for occurrence of an 8 bp sequence in a genome of this size.