RESUMO
Two populations of Escherichia coli, each initiated with a single clone containing a derivative of the plasmid pBR322, were maintained for long periods in glucose-limited continuous culture. In both populations, after an extensive number of generations had elapsed, clones were isolated in which the transposon Tn3 from the plasmid had integrated into the bacterial chromosome. In both cases examined, the transpositions were shown to increase relative fitness approximately 6-7%, in the environment in which the populations were maintained. The loci of integration were mapped to approximately 13.2 min (population 1) and approximately 32.8 min (population 2).
Assuntos
Escherichia coli/genética , Evolução Biológica , Mapeamento Cromossômico , Cromossomos Bacterianos , Elementos de DNA Transponíveis , DNA Bacteriano/genética , Plasmídeos , Transdução GenéticaRESUMO
Thirteen independent populations of Saccharomyces cerevisiae (nine haploid and four diploid) were maintained in continuous culture for up to approximately 1000 generations, with growth limited by the concentration of organic phosphates in medium buffered at pH 6. Analysis of clones isolated from these populations showed that a number (17) of large-scale chromosomal-length variants and rearrangements were present in the populations at their termination. Nine of the 16 yeast chromosomes were involved in such changes. Few of the changes could be explained by copy-number increases in the structural loci for acid phosphatase. Several considerations concerning the nature and frequency of the chromosome-length variants observed lead us to conclude that they are selectively advantageous.