Time mapping is performed in a cross involving the genes his, leu, mal, and xyl.

Question

Time mapping is performed in a cross involving the genes his, leu, mal, and xyl. The donor cells are prototrophs and the recipient cells are auxotrophic for all four genes. The experiment is interrupted at 5-minute intervals for 30 minutes and the following data are obtained: (a) Create a time map of these genes on the bacterial chromosome. (b) What do the recombination data for the xyI gene suggest about its relative location to the origin of the F factor plasmid? Different Hfr strains of the some bacterial species are created when the F factor inserts itself into different places in the circular bacterial chromosome. Interrupted conjugation experiments are conducted using four different Hfr strains of E. coil. The order of gene transfer (as found in the recipients) is shown below: Assume that gene b is starting point (this is random because the bacterial chromosome is circular) and determine the correct gene sequence based on the data.

Explanation / Answer

1 (A) The units of time maps are in minutes. Only xyl was present in the recepient cells after 5 minutes which means its the first gene on the map. The second gene, mal was seen after 15 minutes so the distance between xyl-mal is 5 mins. Similarly, the third gene, his entered after 20 minutes, therefore the map distance between mal-his is also 5 minutes.

Genes on the bacterial chromosome; OriC---------xyl-------mal------his-------leu

Distance, map units in mins : 5 5 5 5

1 (B) xyl is located nearest to the oriC

2. To find the order of the gene sequences in interrupted mating, you first need to align the similar sequences in he given Hfr strains.

Given the starting point is b, so we will start with strain where the first sequence is b i.e. strains 4.

b-a-c-t

Now, lets move up to strain 3, with the sequence e-r-i-u-m-b. The only common sequences among the two sequences is b so we align it without changing the sequence of either strains.

b-a-c-t

e-r-i-u-m-b

The squence of the second Hfr strain is the, c-t-e-r-i-u. Again aligning the sequences with the already aliged sequences of the first two hfr strains.

  b-a-c-t

e-r-i-u-m-b

c-t-e-r-i-u

Now aligning the first strain, u-m-b-a-c-t

  b-a-c-t

e-r-i-u-m-b

c-t-e-r-i-u

     u-m-b-a-c-t

Therefore, the order of the sequence if b is the starting point is

b-a-c-t-e-r-i-u-m

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.