BIOL2343 S4 2018 Assignment 2: Genetic Mapping in Prokaryotes 1 Question 1 An experiment was carried out in E. coli mapping five genes around the...

BIOL2343 S4 2018

Assignment 2: Genetic Mapping in Prokaryotes

1

Question 1

An experiment was carried out in E. coli mapping five genes around the chromosome with

each of three different Hfr strains. The genetic markers were bio, met, phe, his, and trp. The

Hfr strains were found to transfer the genetic markers at the times indicated below.

(i) Complete the missing data in the table indicated by the question marks.

(ii) Construct a genetic map of the E. coli chromosome that includes all five markers,

the genetic distances in minutes between adjacent gene pairs, and the origin and

direction of transfer of each Hfr.

Hfr l markers bio met phe his

Time of entry 26 44 66 ?

Hfr 2 markers phe met bio trp

Time of entry ? 26 44 75

Hfr 3 markers phe his ? bio

Time of entry 6 27 35 ?

Question 2

Bacteriophage Pl was grown on a wild type strain of E. coli and the resulting progeny phage

are used to infect a strain with three mutations, arg-, pro-, his-, each of which results in a

requirement for an amino acid, either arginine, proline, or histidine, respectively. Equal

volumes of the infected culture were spread on plates containing minimal medium

supplemented with various combinations of the amino acids, and the number of colonies

appearing on each plate was counted. The results are shown below. Note - in each row, the

+ signs indicate the amino acid is present in the media.

Supplements

-------------------------------------------------

Plate number Arginine Proline Histidine Number of colonies

1 + + 0 1000

2 + 0 + 1000

3 0 + + 1000

4 + 0 0 200

5 0 + 0 100

6 0 0 + 0

-ve control 0 0 0 0

+ve control + + + 1000

(a) For each of the six types of medium, list the donor markers that must be present

to allow the transduced cell to form colonies.

(b) Using these results, construct a genetic map of the arg, pro, his region showing

the relative order of the genes and the cotransduction frequencies between the

markers.

BIOL2343 S4 2018

Assignment 2: Genetic Mapping in Prokaryotes

2

Question 3.

A cotransduction study involving five bacterial loci, a, b, c, d, and e, is carried out.

Transductants are initially selected on the basis of the a gene. The frequency with which each

of the other four genes is cotransduced with a is as follows: a with b, 47%; a with c, 56%; a

with d, 63%; and a with e, 64%.

(a) Based on a quick inspection of these cotransduction frequencies what general

statement can be made about the degree of linkage between these loci?

(b) Assuming the differences in these cotransduction frequencies to be statistically

significant, what do they suggest about the order of these five loci?

(c) The relative positions of two of these loci cannot be reliably stated. Identify these

two loci and explain why their positions cannot be stated reliably.

(d) Can you suggest how you might go about determining the order of these two loci?