4. At time 0 an Hfr strain was mixed with an F- strain, and at various times aft

Question

4. At time 0 an Hfr strain was mixed with an F- strain, and at various times after mixing, samples were removed and agitated to separate conjugating cells. The cells were then plated onto medium containing streptomycin and the number of prototrophic recombinants for each of the markers was determined. The cross may be written as Hfr a b c' d'e f g'h' str X F a b c d e f gh str (NO ORDER IS IMPLIED) The graph of the number of recombinants against time is shown below. 100r % str recombinants so 5 10 15 20 25 Minutes after start of conj ugation Based on these data, which of the following statements is TRUE: A. h'and e are farther apart on the bacterial chromosome than b' and a B. Most e strr recombinants are likely to be Hfr cells. C. All F cells which received a from the Hfr in the chromosome transfer process must also have received b D. The order of gene transfer from Hfr to F is FIRST at then g', then b', then e', then h

Explanation / Answer

By looking at the graph we can conclude the following things:

1- h+ is present in all the recipient strains.

2- the number of conjugant which has a+ are the least in number.

3- Distance between h+ and a+ is the highest as they are farthest to each other.

4- Order of gene transfer is h+, e+, b+, g+ and a+

Option A is wrong h and e are closer than b and a.

OPtion D is wrong. as the order of gene transfer is h+, e+, b+, g+ and a+

Option B is wrong - most h+ are most likely to be Hfr

option C is correct- b+ is transferred before a+. So if the conjugate has a+ then it must have b+ in its genome.

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