At Time Zero,an Hfr Strain (Strain 1)was Mixed with an F^-

question 15

Essay

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:
HFr 1: $a ^ { + } b ^ { + } c ^ { + } d ^ { + } e ^ { + } f ^ { + } g ^ { + } h ^ { + } S t r ^ { 5 }$
$\mathrm { F } :$$a^{-} b^{-}-d^{-} e^{-}f ^{-}g^{-}h^{-}S tr{ }^{R}$

No order is implied in the above listing.The samples were then plated onto selective media to measure the frequency of h⁺Str^R recombinants that had received certain genes from the Hfr cell.The following graph shows the percentage of recombinants against time in minutes.
a)Draw a linear map of the Hfr chromosome indicating:
(1)the point of insertion (origin).
(2)the order of the genes a⁺,b⁺,e⁺,g⁺,and h⁺.
(3)the shortest distance between consecutive genes on the chromosome in minutes.
b)An additional four Hfr strains (strains 2 $\times$ 5)were obtained.Each carried the wild-type alleles of the genes listed below.They were mated individually to the same F^- strain shown above (carrying the recessive alleles of all genes).With interrupted mating,the times of first appearance in minutes of individual Hfr markers in exconjugants were determined,as shown in the following chart.
$\begin{array}{ll}&\text { Minutes }\\\text { Hfr marker }& \mathrm{Hfr} 1& \mathrm{Hfr} 2 &\mathrm{Hfr} 3 &\mathrm{Hfr} 4 &\mathrm{Hfr} 5\\a^{+} && 2&&20 \\b^{+} && &11\\c^{+} & &12 &28&10\\d^{+} & &24&&&5\\e^{+} &&&&35&50 \\f^{+} &&&88&&35\\g^{+} &\\h^{+} \end{array}$

Draw the genetic map showing:
(1)the positions of genes a $\times$ through h.
(2)the origins of the Hfrs (including strain 1).
(3)the orientation of the origins.
(4)the shortest distance between consecutive genes or origins.

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Definitions:

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Ileum

The last section of the small intestine.

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The semi-fluid mass of partly digested food that is passed from the stomach to the small intestine for further digestion.

Small Intestine

The part of the digestive tract that absorbs nutrients and minerals from food, extending from the stomach to the large intestine.