Problem Set 10, Fall 2015
Name:
8 points total
1. A Hfr strain possessing the markers his+ met+ tyr+ strs was mated with a F– strain possessing the markers his–
met– tyr– strr. The time of entry for each marker is shown below.
Donor Marker
his+
met+
tyr+
Time (min)
21
12
46
a. Based on the results draw a map of the Hfr chromosome. Indicate the position of the F element, and
the first marker to be transferred.
12
met
9
his
hfr
25
tyr
b. On what type of plates were cells grown to determine the above information?
–His + Strep
–Met + Strep
–Tyr + Strep
1
Problem Set 10, Fall 2015
Name:
8 points total
2. In three different interrupted mating experiments, you obtain the following data for the time of entry of the
following genes: arg, met, leu, ser, gal, val, and phe. All of these experiments were conducted using Hfr
strains (Hfr 1, Hfr 2, and Hfr3) derived from the same original strain of E. coli.
Experiment 1 (Hfr 1)
Met
10 min
Val
25 min
Leu
30 min
Arg
40 min
Ser
55 min
Gal
60 min
Experiment 2 (Hfr 2)
Experiment 3 (Hfr 3)
Gal
5 min Leu
5 min
Ser
10 min Val
10 min
Leu
35 min Met
25 min
Val
40 min Phe
55 min
Met
55 min Gal
75 min
Phe
85 min Ser
80 min
a. Determine the order of these genes on the bacterial chromosome and draw a single map showing the position
of each of these genes on the bacterial chromosome. Based on the time intervals above, indicate the map
distances between each gene, expressed in minutes. Also show the origin of transfer and direction of transfer
for each Hfr.
hfr1
10
met
15
val
5
leu
5
hfr3
5
arg
20
15
ser
phe
5
15
5
gal
hfr2
b. If the crosses were set up as described in class, what are the genotypes of the donor and recipient cells?
Donor: Hfr arg+ ser+ gal+ phe+ met+ val+ leu+ strpS
Recipient: F- arg- ser- gal- phe- met- val-1 leu- StrpR
2
Problem Set 10, Fall 2015
Name:
8 points total
3. In three different interrupted mating experiments, you obtain the data shown below for the time of entry. All
experiments use Hfr strains derived from the same original parent strain.
Hfr1
miy 10 min
sow 20 min
raj
35 min
nub 40 min
tod
50 min
mic 65 min
sha
75 min
Hfr2
sow 5 min
miy 15 min
chr
30 min
sha
40 min
mic 50 min
tod
65 min
nub
75 min
Hfr3
mic 5 min
tod
20 min
nub
30 min
raj
35 min
sow 50 min
miy 60 min
chr
75 min
a. Show the genetic map for each of these genes on the circular chromosome. Indicate the location of
each origin and the direction of transfer. Doesn’t need to be drawn to scale.
hfr1
5
chr
10
sha
5
hfr3
5
mic
10
15
miy
tod
10
10
sow
nub
5
5
10
raj
hfr2
b. What are the genotype of the donor and recipient strains?
Hfr miy+ sow+ raj+ nub+ tod+ mic+ sha+ chr+ StrS
F– miy- sow- raj- nub- tod- mic- sha- chr- StrR
3
Problem Set 10, Fall 2015
Name:
8 points total
4. The exotic tropical tree frog E. qinae normally has 13 pairs of chromsomes (i.e. 2n = 26). You find a number
of unusual individuals with the chromosome content shown below. Please fill in the blanks for each of the
variants in the table below:
# chromosomes
ploidy of individual
25
monosomy
13
monoploid
28
could be double trisomy or tetrasomy
52
tetraploid
27
trisomic
5. In an interrupted mating mapping experiment, you obtain the results shown in the graph below. The
experiment was conducted as described in class.
a. Show the genetic map for each of these genes on the circular chromosome. Indicate the location of the
origin and the direction of transfer. Doesn’t need to be drawn to scale.
hfr
trp
3
4
met
7
leu
7
arg
5
lys
b. What are the genotypes of the donor and recipient strains?
donor: Hfr trp+ met+ leu+ arg+ lys+ StrS
recipient: F- trp- met- leu- arg- lys- StrR
c. For each gene, the number of recombinants increases with time until they reach a maximum. Why
does the number of recombinants for a given gene increase with time?
The matings to not all begin at the same time.
d. Why does the number of recombinants reach a maximum?
The probability of separation is balanced by the probability of new matings.
4
Problem Set 10, Fall 2015
Name:
8 points total
6. Compare and contrast the three modes of bacterial DNA transfer.
Conjugation – involves direct cell-cell contact through a cytoplasmic bridge. Involves transfer of
fertility factor (F+), part of bacterial chromosomes (Hfr) or F’
transformation – involves take up of free DNA from the environment, no direct cell-cell contact
transduction – transfer of DNA between bacteria by virus, no direct cell-cell contact
7. In a transduction mapping experiment, you get the following results.
experiment
1
2
selected marker
a+
b+
unselected markers
15% b+, 30% c+
30% c+, 15% a+
a. Draw the relative position of a, b and c.
a
c
b
b. a, b and c are enzymes required for the synthesis of A, B and C, respectively. An a mutant can’t grow
without A in the media, etc. How are the above recombinants identified?
In experiment 1, cells were plated on plates that lacked A and then replica plated to places that
lacked B and plates that lacked C. In experiment 2, cells were plated on plates that lacked B and then
replica plated to plates that lacked A and plates that lacked C.
8. In studying a particular animal, you find that the fourth chromosome is unusual. The two copies of
chromosome 4 are shown. The normal
chromosome is shown on the top, and the
unusual one is shown on the bottom. The
position of seven genes is shown.
a. What is the specific name of the chromosomal alteration that generated the abnormal chromosome?
pericentric inversion
b. Show the two chromosomes synapsed in meiosis. Please include the genes.
too hard to draw in the computer, it involves formation of an inversion loop to bring homology
together.
c. What effect will the rearrangement in the unusual chromosome have on recombination? Why?
It will appear to suppress recombination because gametes produced by crossing over in the
inverted region will be inviable.
d. You find an individual homozygous for the abnormal chromosome (i.e. the bottom chromosome).
Show it’s chromosomes synapsed in meiosis. Please include the genes.
5