A professor at the Waksman Institute cultivates orchids' His favorite strain, called W1, has a white

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A professor at the Waksman Institute cultivates
orchids. His favorite strain, called W1, has a
white flower and breeds true. In propagating the
strain, he randomly finds five plants which
produce black flowers among the thousands he is
growing. Knowing that this flower would be a big
seller for funerals, he decides to investigate
these mutant plants in further detail. He calls
these strains B1, B2, B3, B4 and B5.
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a) In the first experiment he back crosses each
black plant with the parental white W1 (wild
type) strain, examines 100 progeny (F1) and gets
the following results Cross P X P F1 1 B1
X W1 100 W. 2 B2 X W1 100 W. 3 B3 X W1
100 W. 4 B4 X W1 100 W. 5 B5 X W1 50 W,
50 B. What can the professor conclude about
each strain from this experiment?
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b. Back cross the progeny Cross Progeny 6 selfed
W progeny from cross 1 26B, 74W 7 selfed W
progeny from cross 2 24B, 76W 8 selfed W
progeny from cross 3 6B, 94W 9 selfed W
progeny from cross 4 25B, 75W 10 selfed B
progeny from cross 5 77B, 23W 11 selfed W
progeny from cross 5 100W What can the
professor further conclude about each strain (B1,
B2, B3, B4 and B5) from this experiment? Explain
the results of each cross.
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c) He then performs crosses between each of the
original strains and gets the following
result B1 B2 B3 B4 B5 W1 B1 100B 100W 100W 1
00B 50B, 50W 100W B2 100B 100W 100W 49B,
51W 100W B3 100B 100W 50B, 50W 100W B4 100B
51B, 49W 100W B5 74B, 26W 51B,
49W W1 100W What can the professor further
conclude from this experiment?
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d) Suppose a transformation system had been
developed for these orchids. How would he
identify the gene that caused the mutant
phenotype in each mutant? (i.e. How would you
clone the genes?)
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502 Lecture 2 Bacterial Genetics I Gene
Transfer and Mapping I Birth of molecular
biology 1. Major advances in molecular genetics
-late 50's-60's Structure of DNA Codons and
deciphering the genetic code Fine structure
mapping of a gene Genetic regulation Lag in
the 80's and early 90's, little
funding Resurgence in interest in bacterial
systems Re-emphasis on basic research and
systems Antibiotics are becoming less
functional Genomics
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Information on Microbial Species at NCBI
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Links to Information on Completed Microbial
Genomes
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Taxonomy and Homology of Genes in the Genome
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Information on Gene Products
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Location of Genes According to Function
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Prokaryotic Cell Structure
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Bacterial Cell Division
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Mutants that Affect Cell Division
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Bacterial Growth Rates
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Bacteria as a Genetic System
Frequency of mutations is rare, need a way to
identify mutants

• Mutant Phenotypes
• Auxotrophs Requires a component - adenine,
  threonine
• Prototroph (Wt) - Ability to grow in the absence
  of a component

How do you identify something that doesn't grow?
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Duplicating the colonies on a plate
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Genetic Screen (growth or color assay)
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Genetic Selection (drug resistance, phage
immunity)
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Bacterial mating
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Mating requires physical contact of cells
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Direction of Transfer Experiment
Str
Str
-

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Ability to Transfer DNA Depends on the F Factor
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Interconversion of F to Hfr to F''
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Transfer of F' Markers - Complementation
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Transfer of Hfr' Markers - Recombination
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Recombination of Markers
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Blender Experiment - Wollman and Jacob
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Hfr integrate at different positions in the
genome - Transfer different markers
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Mapping the genes in a chromosome
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What is the order of the genes?
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Generalized Transduction - Lederberg Zinder 1951
Performed conjugation with Salmonella Found
prototrophs in U-tube experiment Did not with
smaller filter Determined it was the
bacteriophage P22 that transferred DNA
markers.
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Temperate Bacteriophage Life Cycle
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Generalized Phage Transduction - Lederberg
Zinder Working with P1 phage
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Specialized Transduction - Genes near an
integration site
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Transformation - Griffith (1928) Streptococcus
pneumoniae Avery (1944) Determined it was
DNA Will only get cotransformation of closely
spaced markers
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Genetic map of the E. coli chromosome