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    Hfr strains

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    In E.coli, four streptomycin-sensitive, prototrophic Hfr strains were mated with a stretomycin-resistant F^- strain auxotrophic for a number of nutritonal requirements. Matings were interrupted at various intervals, and cells were plated on streptomycin-containing minimal meduim supplemented with particular nutrients to test for gene transfer. Entry time (in minutes) of the first five genes for the four strains were as follows:
    Hfr strain 1 : M+ (4), Z+(6), X+(11), W+(15),C+(17.5)
    Hfr strain 2 : L+ (1), A+ (2), N+(5), C+ (6.5), W+(9)
    Hfr strain 3 : A+(2.5), L+(3.5), B+(6), R+(11.5), U+ (15)
    Hfr strain4 : Z+ (3), M+(5), U+ (11), R+(14.5), B+(20)

    draw the map of the E.coli genome consistent with the data. Include distances between the genes and indicate the insertion points of the F plasmid in each Hfr strain.

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    Solution Preview

    GENETIC MAPPING OF BACTERIAL GENOME THROUGH CONJUGATION WITH F PLASMID

    Hfr strain 1 : M+ (4), Z+(6), X+(11), W+(15),C+(17.5)
    Hfr strain 2 : L+ (1), A+ (2), N+(5), C+ (6.5), W+(9)
    Hfr strain 3 : A+(2.5), L+(3.5), B+(6), R+(11.5), U+ (15)
    Hfr strain4 : Z+ (3), M+(5), U+ (11), R+(14.5), B+(20)

    If you look at the four strains, you will find a pattern emerging. All the genes are in the same order. For example look at strain 1 and strain 2. They both have a C and W gene next to each other, but in the opposite direction. Therefore, they represent a match but going in the opposite direction. Therefore, from ...

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