Question

You isolate a variant of the Hfr parent in question 6 that only shows recombination of the his+ and trp+ genes. The cross was ( HFR lac+, gal+, trp+, his+, strr X F- lac-, gal-, trp-, his-, strs ). This strain most likely:_________.

a. Contains an F' his+ trp
b. Has become F-
c. Contains an Hfr translocation
d. No longer mates as a merry diploid
e. Not enough information is given

Answer 1

The correct answer is - b. has become F-.

Step-by-step explanation:

In the case of the cross of two different strains, some genetic material moves to the F- strain from the Hfr strain, but due to genome size, it's not possible that all the genes can pass into a single bacterium.

Instead of complete transfer, each individual F- cell gets a different and random subset of genes from the Hfr. There is no translocation and F' does not contain his+ trp+.