An Extraterrestrial Scientist Is Trying to Obtain a Genetic Map

question 34

Essay

An extraterrestrial scientist is trying to obtain a genetic map of a newly discovered bacterium using standard techniques such as interrupted conjugation and Hfr mapping.She is particularly interested in three loci (ata,tic,and lan)encoding proteins that are required for the synthesis of atanine,ticovine,and lancytrine (three essential extraterrestrial amino acids),respectively.With the help of interrupted-conjugation experiments,the scientist determines that ata is the last marker to enter the recipient bacterium.
She now sets up a cross between a wild-type Hfr strain that is tertacycline sensitive and an ata^-tic^-lan^- F^- strain that is tetracycline resistant.5000 exconjugants are recovered on minimal medium plus tetracycline,ticovine,and lancytrine,and subsequently replicated onto a variety of media.
The results are as follows:
- minimal medium and tetracycline: 4704 colonies grow;
- minimal medium plus lancytrine and tetracycline: 4708 colonies grow;
- minimal medium plus tetracycline and ticovine: 4900 colonies grow.
a)Draw a genetic map of these three loci (including all the map distances).
b)Why is the scientist using tetracycline on her plates (what is the purpose)?
c)Why is she recovering the exconjugants on plates that lack atanine?

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