GENETICS TEST 3 CHAPTER 8 Bacteriophages viruses that use bacteria as their hosts Bacteria essential research organisms Have short reproductive cycles Mass produce Can be studied in pure cultures a single species or mutant strain of bacteria or one type of virus can be isolated and studied independently Bacteria and viruses usually contain only a single chromosomes and are haploid All mutations are expressed directly in all descendent of mutant cells Bacteria grown in a petri dish on semisolid agar surface or liquid culture medium Minimal Medium nutrient components are simple and only organic carbon source and ions present as inorganic salts Bacterium must be able to synthesize all essential organic compounds Prototrophs Wild type for all growth requirements His Auxotroph components through mutation His Mutant strain that loses the ability to synthesize one or more organic Serial Dilution if the number of colonies is too great to count on a petri dish a series of successive dilutions of the original liquid culture is made and plated until the colony number is able to be counted The process of genetic recombination in bacteria provided the basis for the development of chromosome mapping methodology Genetic recombination applied to bacteria the replacement of one or more genes present in the chromosome of one cell with those from the chromosome of a genetically distinct cell Alters genotype Vertical Gene Transfer when a transfer occurs between members of the same species Horizontal Gene Transfer when a transfer occurs between members of related but distinct bacterial species Genes confer survival advantages to the recipient species Conjugation a process by which genetic information from one bacterium is transferred to and recombined with that of another bacterium Joshua Lederberg and Edward Tatum 1946 Grew two separate strains on separate supplemented media and then cells from both were mixed and grown together for several generations and then grown on minimal media must be prototrophs Concluded that any prototroph that had arisen was a result of some form of genetic exchange and recombination of two mutant strains F Cells when cells serve as donors of parts of their chromosomes during unidirectional transfer F stands for fertility F Cells recipient bacteria receive the donor chromosome material now known as DNA and recombine with part of their own Cell contact is essential for chromosome transfer to occur Bernard Davis Davis U tube grows F and F Sintered glass filter at the base of the tube with pore size that allows passage of the liquid medium but too small for bacteria to pass F is placed on one side of the filter and F on the other He moved the medium around but when he put samples from F and F sides on minimal medium no prototypes were found so he concluded that there must be physical contact F pilus sex pilus F factor confers the ability to donate part of their chromosome during conjugation but can be eliminated in certain conditions Really a plasmid that is capable of integration into the chromosome If the infertile cells are then grown with fertile they can regain their F factor Consists of circular episome and has a double stranded helix that separates during conjugation One strand goes to recipient but both strands are replicated so that the donor and the recipient become F cells Episome genetic molecule that can replicate either in the cytoplasm of a cell or as part of its chromosome Hfr high frequency recombination Behave as donors conjugate and form a F pili but are a special type of F cells Donor cells never become Hfr strain but instead remain at F unlike F making F F F X F F Hfr X F F The F factor is nicked in the middle during single strand transfer and because the entire strand is not transferred it stays a F To get the whole factor the whole strand must be transferred Display nonrandom pattern of recombination in any given strain certain genes are more frequently recombined than others and some not at all F State an F factor can lose its integrated status causing the cell to revert to the F state The F factor frequently carries several adjacent bacterial genes along with it Hfr F Cells with bacterial genes in cytoplasm that causes the F bacterium to act like a F cell by initiating conjugation with F The F factor that contains chromosomal genes is then transferred to the F and are now present as duplicated in recipient cell Creates a merozygote Francis Jacob and Elie Wollman Gene mapping by interrupted conjugation interrupted mapping technique Specific genes of a given Hfr strain were transferred and recombined sooner than others The transfer times indicate the order and relative distances between genes and can be used to construct a genetic map Different Hfr strains have the F factor integrated at different sites and in different orientation 100 min to transfer whole e Coli chromosome Rec genes recombinant genes Transformation mechanism for recombining genetic information in some bacteria DNA is extracellular external and is taken up by a living bacterium potentially leading to a stable genetic change in the recipient cell Does not require cell to cell contact like conjugation Can be used to map bacterial genes Can occur naturally DNA from dead cells in the environment can be taken up Process divided into 2 categories Entry of DNA into the recipient cell Recombination of the donor DNA with its homologous region in recipient Only bacterial cells in a state of competence take up DNA Passage into the cell is an active process that requires energy and specific transport chromosome molecules After entry one of the strands of DNA is digested and the other is used in transformation Aligns with complementary region of bacterial chromosome Once integrated the recombinant region contains one host strand originally there and mutant strand Helical region now called a heteroduplex strands from different regions Genes very close together on a bacterial chromosome can be carried together and cotransferred said to be linked Rate of cotransformation is directly proportional to distances between genes If the genes are not close together simultaneous transformation occurs only as a results of 2 independent events involving 2 distinct segments of DNA Bacteriophages phages viruses that have bacteria as their hosts Transduction Bacteriophage T4 of virus Genetic material is contained within an icosahedral protein coat making up head Life cycle initiated when virus binds by