Question

An Hfr strain of E. coli with genotype a+b+c+d+e+f+ is mated with an F¯ auxotrophic strain with the genotype a¯b¯c¯d¯e¯f¯. Conjugation is stopped at 10 minute intervals and the genotypes of the resulting conjugants are determined. The following results are obtained:

after 10 minutes e+

after 20 minutes a+ e+

after 30 minutes a+ b+e+

after 40 minutes a+b+d+e+

after 50 minutes a+b+c+d+e+

after 60 minutes a+b+c+d+e+f+

Which represents the correct order of genes on this bacterial chromosomes?

1. efabcd
2. eabdcf
3. abcdef
4. fedcga
5. cdefab

Answer 1

with a difference of 10 minutes in the conjugation time one gene is passed to the F- bacteria

after 10 minutes e+

after 20 minutes a+ e+ ( order is ea)

after 30 minutes a+ b+e+ ( order is eab)

after 40 minutes a+b+d+e+ ( order is eabd)

after 50 minutes a+b+c+d+e+ ( order is eabdc)

after 60 minutes a+b+c+d+e+f+ ( order is eabdcf)

from this data the order of the genes is e+a+b+d+c+f+

so the answer is b) eabdcf