Question

Question 12






An Hfr strain with the genotype cys+ leu+ met+ strS is mated with an F- strain carrying the genotype cys- leu -met- strR .


In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:


Medium 1: Minimal medium plus leucine, methionine, and streptomycin
Medium 2: Minimal medium plus cysteine, methionine, and streptomycin
Medium 3: Minimal medium plus cysteine, leucine, and streptomycin


Question: What donor gene is the selected marker in Medium 1?



A. leucine



B. streptomycin



C. methionine



D. cysteine



E. pleiotropy


Question 2: Select the genotypes of the bacteria that are able to grow on Medium 1:



A.cys- leu- met+ strR



B.cys+ leu+ met+ strR



C. cys+ leu+ met- strR



D.cys- leu+ met- strR



E. cys- leu+ met+ strR



F. cys- leu- met- strR



G. cys+ leu- met+ strR



H. cys+ leu- met- strR



Question 3: Select the genotypes of the bacteria that are able to grow on Medium 3:



A.cys- leu- met+ strR



B.cys+ leu+ met+ strR



C.cys+ leu+ met- strR



D.cys- leu+ met- strR



E. cys- leu+ met+ strR



F.cys- leu- met- strR



G.cys+ leu- met+ strR



H.cys+ leu- met- strR


Question4: What is the purpose of adding streptomycin to each selection medium?



A.to ensure that no accident contamination will germinate on the media



B.to ensure that only exconjugate bacteria and not donor bacteria will grow on the media



C.to prevent the exconjugate bacteria from overgrowing and running out of supplements



D.to interrupt the mating experiment at the appropriate time to collect all data needed



E.all bacteria need streptomycin to grow

Answer 1

2. H