In an Hfr X F- cross, leu+ enters as the first marker, but the order of...

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In an Hfr X F- cross, leu+ enters as the first marker, but the order of...

In an Hfr X F- cross, leu+ enters as the first marker, but the order of the other markers is unknown. If the Hfr is wild-type and the F- is auxotrophic for each marker in question, what is the order of the markers in a cross where leu+ recombinants are selected if 27 percent are ile+, 13 percent are mal+, 82 percent are thr+, and 1 percent are trp+?

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Answer 1

Answer #1

THE COMPLETE ORDER IS:

leu+
thr+
ile+
mal+
trp+.

REASON

The natural gradient of transfer is created by a spontaneous breakage which makes it less likely for a recipient to receive later and last markers. As we have selected for the initial marker in this cross,

The frequency of recombinants = fn(order of entry for each marker)

From the above conclusion,it is easy for us to determine the order of the genetic markers by just looking at the percentage of recombinants for any marker among the leu⁺ recombinants. As the inheritance of thr+ is the highest, it should be the first marker to enter after leu+.

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Answer 2

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