Genetics 3301

Chapter 5: Bacterial and Phage Genetics

Bacterial nomenclature:

Ä Plating bacteria on media to isolate individual colonies (5-2); prototrophic bacteria can grow on minimal (salts, carbon source, water) media; auxotrophs must have media supplemented with certain nutrients; resistant mutants will be able to withstand inhibitors like antibiotics (T5-1); A single circular chromosome is found in most bacteria; Additional episomes are called plasmids that are also circular.

Conjugation:

Ä Conjugation is one form of gene transfer in bacteria; Demonstration of conjugation using two auxotrophic strains (5-4); Conjugation requires physical contact (5-5); Donor strains have a fertility (F) factor (they are F⁺) and recipients are F^-; The F plasmid is needed to form a pilus that mediates transfer of the plasmid to a recipient strain (5-7); If the F plasmid is integrated into the chromosome, some of the chromosome can be transferred at a high frequency (Hfr) (5-8); The F plasmid can integrate into the chromosome at different sites, each staring at a specific origin (5-12); Genes can be mapped by measuring the time (in minutes) it takes to transfer a marker from Hfr to and F^- strain (interrupted mating) (5-11); Chromosome transfer only occurs in one direction (5-13); If the original and terminus are both transferred the recipient can become an Hfr; R factors are similar to F, except they carry resistance genes.

Ä Recombination occurs between the donor chromosomal DNA and the recipient chromosome in merozygotes (5-10); Recombination distances can be calculated from the % recombinants between markers when all markers have entered the host (5-16); Fπ episomes carry part of the chromosome and carry any markers to F^- cells with high frequency (5-17).

Transformation:

Ä Exogenous DNA can be used to convert one genotype to another in a process called

transformation; only competent bacteria can be transformed (5-19).

Bacteriophage genetics:

Ä Phage infect bacterial cells by inserting their DNA (5-20); Phage lytic cycle (5-23); When plated on bacterial cells phage form plaques due to lysis; plaque morphology depends on the phage genotype (5-26); phage genes can be mapped by coinfecting bacteria (5-25).

Transduction:

Ä Generalized transduction is the ability of phage to carry pieces of the bacterial chromosome in their phage heads and is due to faulty head stuffing (5-27); cotransductants can be used to map distances between genes (5-28); virulent phages only have a lytic cycle; temperate phage have a lysogenic cycle where phage DNA is integrated into the bacterial chromosome (forming a prophage) and can be induced to lyse the phage; lambda phage are common lysogenic phage that integrate into the E. coli chromosome at specific attachment sites (5-30); specialized transduction occurs by transfering nearby genes after induction of the lytic cycle (5-31).

Key terms: Know all of these except endogenote, exogenote, selective system, screen and zygotic induction.

Problems: 1-6, 8, 13, 16, 17, 20, 21, 23.