Question

Consider an experiment in which an Hfr strain of E. coli bacteria with the StrS, his+, met+ alleles in its genome is mixed with an F- strain of E. coli with the StrR, his-, and met- alleles in its genome. After the cells have been cultured together for 8 hours, the mixture of cells is plated on minimal media containing Streptomycin.
1. Which genotype do you expect to be most common among the colonies that grow?
O F+: StrR, his+ and met+
O F-: StrR, his- and met-
O Hfr: StrR, his+ and met+
O F-: StrR, his+ and met+
O F+: StrR, his- and met-

Answer 1

Answer:

F-: StrR, his+ and met+

Explanation:

Since it is stated that the minimal media contains Streptomycin, therefore:

a.) To be able to grow on this media, the E. coli genome must have StrR allele.

b.) Also remember that only prototrophs can grow on minimal media, thus colonies with mis+ and met+ (which are prototroph) will be the common growth .

c.) In the conjugation of F- strain with an Hfr strain,  F- which contains  the StrR allele do not and cannot form F+ or Hrf strains but remains F-