Question

Read the statements below and state whether it is True or False :

At time zero, an Hfr strain (strain 1) was mixed with an F' strain and various times after mixing, samples were removed and agitated to separate conjugating cells. The cross may be written as Hfr 1:$a^{-}{b}^{-}{c}^{-}{d}^{-}{e}^{-}{f}^{-}{g}^{-}{h}^{-}St{r}^R$, no order is implied in the above listing.

The samples were then plated onto a selective media to measure the frequency of $hSt{r}^R$ recombinants that had received certain genes from the Hfr cell.

The graph shows the percentage of recombinants against time in minutes.

The order of gene transfer from Hfr to F was $a^{+}$ (first), then $g^{+}$, then $b^{+}$, then $e^{+}$ and $h^{+}$.

• A. True
• B. False

Answer 1

The correct option is B False

With increasing mating time, new alleles enter the F${}^{-}$ cells from the Hfr cells. As is visible from recombination frequency, the h allele first appears among recombinants after about zero minutes of mating, whereas a allele last enters the F${}^{-}$ cells after about sixteen minutes. This means the sequence of entry of loci into the F${}^{-}$ cells from the Hfr is h, e, b, g and a. The given sequence is not true.