Questions 8 and 9 pertain to the following. Four E. coli strains of genotype a +
ID: 38740 • Letter: Q
Question
Questions 8 and 9 pertain to the following. Four E. coli strains of genotype a+b? are labeled 1, 2, 3, 4. Four strains of genotype a?b+ are labeled 5, 6, 7 and 8. The two genotypes are mixed in all possible combinations and (after incubation) are plated to determine the frequency of a+b+ recombinants. The results indicated in the table are obtained, where M = many recombinants, L = low numbers of recombinants, and 0 = no recombinants. The strains can be classified as 3 types relative to conjugation: either F?, F+ or Hfr with regard to a and b gene transfer.
8. Which of the following can be classified as F- cells?
a) 2, 5, 7; b) 2, 3, 6; c) 1, 4, 6; d) 3, 8; e) none of the above.
9. True or false. Suppose after mixing strains 2 and 8 the culture was left to grow on medium missing the nutrients needed by the a- and b- mutants. Virtually all of the cells arising from the minimal media plate would be expected to have pili if examined under the electron microscope.
strains
1
2
3
4
5
L
0
M
L
6
0
L
0
0
7
L
0
M
L
8
0
M
0
0
strains
1
2
3
4
5
L
0
M
L
6
0
L
0
0
7
L
0
M
L
8
0
M
0
0
Explanation / Answer
Hi,
8) Option a (2 ,5 , 7) is the answer
F- strain responds differently when compared to F+ and Hfr strains.
Strains Hfr X Hfr, F+ X F+, F- X F-, Hfr X F+ would give 0.
Therefore, strains 2,5,7 are F-; 1,4,6 are F+ while 3 and 8 are Hfr.
9) i guess this is True (not so sure about this)
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