Article Abstract:
Theeffects of Ty1 transposition in populations of Saccharomyces cerevisiae were assessed in regard to their effects on fitness. Initial experiments showed thatthe average effect of Ty1 transposition is deleterious to the population. However, along with this general decreased fitness, an increase in population density variance with increased Ty1 copy number was also observed. Further experiments showed that in 98-112 generations, the frequency of zero Ty1 copy number clones decreased to zero. The results indicate that Ty1 transposition results in average decreased fitness, but is also responsible for introducing mutations which may advantageous.
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Article Abstract:
Transposon Tn3 was transposed from the plasmid to the chromosomes of two independent populations of Escherichia coli grown in glucose-limited conditions after several generations. The E. coli populations contained a single clone of plasmid pBR322 derivative that carried the transposable DNA sequences. The transposed DNA fragments were similar in sizes but differed in their insertion sites in the two bacterial populations. The transpositions conferred to an increase in relative fitness in the environment inhabited by the E. coli populations.
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Article Abstract:
A study of reversion to Lys+ prototrophy in haploid yeast strains that contain a defined mutation showed early appearing Lys+ colonies in independent cultures randomly reverted to prototrophic mutations. Late appearing Lys+ colonies, however, reverted after selective plating. Cells were plated on a synthetic medium which was complete but for lysine. Lys+ prototrophic reversion did not occur when either tryptophan and leucine, or lysine and tryptophan were excluded from the medium.
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