In: Biology
A Hfr strain possessing the markers His+ Met+ Tyr+ Strs was mated with a F– strain possessing the markers His– Met–Tyr– Strr.The time of entry for each marker is shown below.
Donor Marker Time (min)
his+ 21
met+ 12
tyr+ 46
a. Based on the results draw a map of the Hfr chromosome. Indicate the position of the F element, and the first marker to be transferred.
b. On what type of plates were cells grown to determine the above information?
Ans:
a. If the marker takes less time, it is the first marker that enters into the recipient cell and cloest to F element. So, according to data, met+ is the first marker incorporated into recipient cell, followed by his+ and tyr+. So, the marker order is -F-met+-his+-tyr+. A drawing of map of the Hfr chromosome is given below-
b.
After 21 minutes, the cells grown on plate of minimal medium that lacks histidine and present of streptomycin (his- Strr)/ plate of minimal medium that lacks methionine and histidine and present of streptomycin (met- his- Strr).
After 12 minutes, the cells grown on plate of minimal medium that lacks methionine and present of streptomycin (met- Strr).
After 46 minutes, the cells grown on plate of minimal medium that lacks tyrosine and is streptomycin resistant (his- Strr)/ plate of minimal medium that lacks methionine, histidine and tyrosine and present of streptomycin (met- his- tyr- Strr).