At time zero, an Hfr strain (strain 1) was mixed with an F- strain, and at vario

Question

At time zero, an Hfr strain (strain 1) was mixed with an F- strain, and at various times after mixing, samples were removed and agitated to separate conjugating cells. The cross may be written as:

What is the order of a+, b+, e+, g+, and h+ in the Hfr chromosome, starting from the origin?

Hf l: a bcdef g h Str F: a bcd efg h Str the frequency of h t + R No order is implied in the above listing. The samples were then plated onto selective media to measure the frequency of h Str recombinants that had received certain genes from the Hfr cell. The following graph shows the percentage of recombinants against time in minutes. 100 h+ 75 %StrR recombinants 50 bt 25 0 51015 20 25 Time in minutes

Explanation / Answer

The graph indicates that a+ is transferred last, starting about 16 minutes after conjugal pairing.

The genes are transferred linearly in the order h+ (starting at 0 minutes), e+ (starting at 2 minutes), b+ (starting at 9 minutes), g+ (starting at 12 minutes), and then a+.

Thus, the order of the genes in Hfr chromosome, starting from the origin is h+, e+, b+, g+, a+.

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