TABLE 20-3 The Dependence of the Fitness Effects of Mutations on Prior Mutations in E. coli Mutation* Number of alleles on which mean Mean proportional mutational effect is increase Positive Negative Negligible g4205a 8 1.4 A42G 12 4 5.9 E104K 15 1 9.7 M182T 8 3 5 2.8 G238S 16 1.0 x 103 "The mutations leading to antibiotic resistance are designated by their nucleotide or amino acid position. Of the 16 possible allelic combinations of the four other sites, the positive, negative, or neutral effects of the mutation are indicated along with the mean proportional increase in fitness for mutations at the indicated site.
Bacterial Genomics
The study of the morphological, physiological, and evolutionary aspects of the bacterial genome is referred to as bacterial genomics. This subdisciplinary field aids in understanding how genes are assembled into genomes. Further, bacterial or microbial genomics has helped researchers in understanding the pathogenicity of bacteria and other microbes.
Transformation Experiment in Bacteria
In the discovery of genetic material, the experiment conducted by Frederick Griffith on Streptococcus pneumonia proved to be a stepping stone.
Plasmids and Vectors
The DNA molecule that exists in a circular shape and is smaller in size which is capable of its replication is called Plasmids. In other words, it is called extra-chromosomal plasmid DNA. Vectors are the molecule which is capable of carrying genetic material which can be transferred into another cell and further carry out replication and expression. Plasmids can act as vectors.
From Table 20-3, would you expect the noncoding mutation g4205a to be fixed before or after the coding mutation G238S in a population of bacteria evolving resistance to the antibiotic cefotaxime? Give at least two
reasons for your answer.
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