an Hfr strain was mixed with an F- strain, and at various times after mixing, sa

Question

an Hfr strain was mixed with an F- strain, and at various times after mixing, samples 4. At time 0 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 t markers was determined. The cross may be written as Hfr: a'bc'd' e fg h'strs x F a b'cd ef g h' str NO ORDER IS IMPLIED) The graph of the number of recombinants against time is shown below. 100 75 recombinants so 25 ht 96 str r bt 5 10 15 20 25 Mirutes after star t of conj ugati on 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 at. 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 a then g', then b', then e', then h"

Explanation / Answer

C. All F- cells which received a+ from the Hfr in the chromosome transfer process must also have received b+.

In the given graph it is clear that h+ is transferred first followed by e+. Thus h+ and e+ are closer than b+ and a+. The order of the transfer is from h+ to a +. Also b+ is transferred befored a+. Thus the F- cells that have received a+ from the Hfr in the chromosome transfer process must also have received b+.

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