mapping by co transduction ,specialized transduction

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Mapping by Co-transductionby Neekita
CharanMICROBIOLOGY
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• COTRANSUCTION is used to determine a genetic
  map of
• Relative distance between genetic marker and
• The order of the marker
• Fact is that the closer genes are to each other
  their probability of being co co-transduced is
  greeter.
• Frequency of co-transduction is equally
  proportional to the distance of two genes.
• When two gene are close to each other ,result
  are ambiguous because of experimental
  uncertainly.
• FOR EXAMPLE consider three gene a, b, and c
• Frequency of cotransduction is determine by two
  factors crosses a-b ,90 a-c ,33 b-c ,32 2
  erre

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• b is closer to a then c.
• Three factor use for determination of the order
  of closely marker.
• Three crosses are shown for three hypothetical
  gene in the first cross
• donor p22 genotype a b- c cross with a- bc-
  recipient in first cross ,Order 1
• In second order
• b- a c cross with b a- c-

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(No Transcript)
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• Double cross has a grater probability of
  occurrence then quadruple.

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• Consider transduction from a donor strain whose
  genotype is A BC- and A -B -C recipient.
• One phenotype is (A) Selected by plating on
  medium lacking substance A and 100 A colonies
  are further testing for the B and C genotype by
  replica plating

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Recombination events generates the various
recombinant genotype

• This recombinant produced by quadruple exchange
  with order 1and double exchange with order 2.

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• Such gene crosses allows determination of gene
  order but not distance
• Main problem in relating recombination
  frequencies to genetic distance is that even when
  two genes are close enough that they can carried
  by single transducing particle.
• Sometime particle carrying one marker and remain
  another marker
• The genetic map of E.coli S. Typhirium are
  divided in to 100 minutes 1 is an arbitrary unit
  aprox. Equal to 50 kb
• Mathematical formula that relate with co
  transduction frequencies to map distances.
• C(1-d/L)3

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• Where c is co transduction frequency
• D is distance between selected an unselected
  marker
• L is the size of the transducing fragment for
  P22 L 1, for P1 2
• And d L-(13 ?? )
• There for P22 distance between two marker is d
  1-(1)(c)1/3
• So for gene A, B and C is
• A 0.38 B 0.12 C