You are interested in mapping the relative positions of three genes in the E. coli genome and have access to several cell types to use for the mapping:

Question

a) Describe F?, F+, Hfr, and F' bacterial cell types.
b) How would you use one or more of these cell types to map genes A, B, and C in the E. coli genome?
c) If you found that the results were A = 10, B = 5, and C = 3 (in the correct units), what could you conclude about the order and proximity of the three genes?
What will be an ideal response?

Answer 1

Answer:
a) F− cells lack the F plasmid; F+ cells contain the F plasmid; Hfr cells have the F plasmid integrated into the bacterial chromosome; F' cells were once Hfr cells, but the F plasmid has become autonomous and may contain chromosomal genes.
b) Interrupted conjugations between an Hfr strain that contains genes A, B, and C and an F− strain that lacks all three genes could be used to map relative positions of the genes. By interrupting the conjugation at various times and assaying for the presence of the genes in the F− strain, you can determine the order in which the genes were transferred and the time in minutes required for the transfer of each gene.
c) C was transferred first followed by B and then A, which represents the relative order in the genome, with the middle gene B being closer to C than to A, based on the times.