Ch. 8 Bacterial Genetics

A scientist is trying to isolate a penicillin-resistant His- bacterial mutant from a mixed population. Please answer the following questions on direct and indirect selection. The researcher inoculates the test population of bacteria onto glucose salts agar containing penicillin and also on nutrient agar containing penicillin. She counts 25 colonies on the glucose salts plate lacking histidine and 32 colonies on the nutrient agar. Which of the following statements is TRUE?

- The colonies on both plates contain penicillin-resistant mutants. Since both types of plates contain penicillin, only penicillin-resistant mutants will grow on - The glucose salts plate contains some mutants. The mutants are the bacteria that cannot grow on the medium lacking all the nutrients required for growth - if there were no mutants, both plates would have had 32 colonies on them.

A culture of E. coli is irradiated with UV light. The UV light affects the cell's DNA by

forming covalent bonds between thymine bases on the same strand of DNA

genotype

genetic makeup of the organism—in other words, the DNA sequence

types of mutations in DNA

Nonsense - A mutation that changes a codon that specifies an amino acid to a stop codon, resulting in premature termination of polypeptide synthesis. Missense - A mutation that results in changing a codon such that a different amino acid is specified. Silent - A mutation that changes a codon into a different codon, but both codons specify the same amino acid; this causes no change in the resulting polypeptide. Frameshift - A mutation resulting from an insertion or deletion of bases that causes a change in the reading frame of the mRNA.

In direct selection methods used to identify possible carcinogens (example: Ames testing), what does it mean when a chemical can cause a bacterium to develop resistance to some environmental condition?

chemical is a mutagen

horizontal gene transfer can occur via

conjugation

Bacterial cells that have been genetically modified to carry an antibiotic resistance gene can be separated from susceptible (non-resistant) microbes by using a ______ selection method using agar plates with antibiotic.

direct

A scientist is trying to isolate a penicillin-resistant His- bacterial mutant from a mixed population. Please answer the following questions on direct and indirect selection. To isolate a His- mutant, the researcher need only inoculate the bacteria onto nutrient agar containing histidine.

false

sequence of Griffith Experiment for Transformation

living encapsulated cells > mouse dies living non-encapsulated cells & heat-killed encapsulated cells > no effect heat-killed encapsulated cells + living non-encapsulated cells > mouse dies & living encapsulated cells isolated

phenotype

organism's observable characteristics like presence of a flagellum

A scientist is trying to isolate a penicillin-resistant His- bacterial mutant from a mixed population. Please answer the following questions on direct and indirect selection. To isolate penicillin-resistant mutants, the scientist must inoculate the parent population on plates containing ______; this approach is ______ selection.

penicillin; direct