Some plasmids can replicate in several distinct species of bacteria. Frequently these plasmids have transposons carrying several different antibiotic resistance genes. In a hospital that has an outbreak of several species of bacteria each carrying resistance to three drugs (streptomycin, gentamicin, and penicillin), what is the best way to determine whether or not this resistance is due to a single shared plasmid with all three resistance genes?
A) Demonstrate that all the resistant bacteria have a plasmid.
B) Isolate plasmids from all resistant bacterial species and demonstrate that drug-sensitive cells from these same species become resistant to all three drugs when this plasmid is transformed. Confirm that the same plasmids are present in all species by sequencing the plasmid DNA.
C) Sequence the genomes of the resistant species and demonstrate mutations in the same homologous genes.
D) Isolate plasmids from one resistant species and transform a drug-sensitive strain of the other bacterial species to see if resistance occurs in the transformants.
B) Isolate plasmids from all resistant bacterial species and demonstrate that drug-sensitive cells from these same species become resistant to all three drugs when this plasmid is transformed. Confirm that the same plasmids are present in all species by sequencing the plasmid DNA.
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Which of the following was observed by Erwin Chargaff?
A. Base composition of DNA does not vary from one species to another. B. The DNA isolated from different tissues of the same species all have the same base composition. C. Base composition changes as the organism ages. D. In all species, the number of adenines equals the number of guanines. E. In all species, A + T = G + C.
A frog sees a fly and immediately sticks his tongue out to catch it. Which type of cell transmitted the visual signal from
his eye to his brain?
a. afferent neuron b. efferent neuron c. interneuron d. motor neuron e. Schwann cell
Sieve tubes are different from vessel members
because they a. do not have nuclei. b. are not connected to each other. c. are alive at maturity. d. conduct minerals. e. fit all of these descriptions.
Why does a female have millions of ovarian follicles as a fetus but has perhaps just over a thousand in her early fifties?
A) Several hundred follicles ovulate per monthly cycle and deplete the follicle supply at a steady rate. B) Natural degeneration of follicles speeds up in later years. C) Several thousand follicles ovulate per monthly cycle and deplete the follicle supply at a steady rate. D) Production of new follicles from stem cells slows in her fifties.