Download BIOL/GEN 313_Wksht_032416

Supplemental Instruction
Leader: Taylor Thomas
BIOL/GEN 313
Instructors: Myers & Vollbrecht
Iowa State University
Date: 3/24/16
_____________________________________________________________________________________________
1.
A series of Hfr strains that have genotype m+ n+ o+ p+ q+ r+ are mixed with an F- strain that has the
genotype m- n- o- p- q- r-. Conjugation is interrupted at regular intervals and the order of the appearance of
the genes from the Hfr strain is determined in the recipient cells. The order of gene transfer for each Hfr
strain is:
Hfr5
m+
q+
p+
n+
r+
o+
Hfr4
n+
r+
o+
m+
q+
p+
Hfr1
o+
m+
q+
p+
n+
r+
Hfr9
q+
m+
o+
r+
n+
p+
What is the order of genes on the circular bacterial chromosome? For each Hfr strain, give the location of
the F factor in the chromosome and its polarity.
2.
Scientists studied via transformation the transfer of genes from a wild type strain to a mutant strain. They
reported the following rates of cotransformation between his+ and other genes (expressed as cotransfer
rate.)
Genes
Rate of Cotransfer
his+ and aro+
0.015
his+ and try+
0.10
his+ and leu+
0.120
his+ and phe+
0.230
his+ and glu+
0.050
On the basis of these data, which gene is farthest away
from his+? Which gene is closest?
3.
A geneticist isolates two mutations in a bacteriophage. One mutation causes clear plaques (c), and the other
produces minute plaques (m). Previous mapping experiments have established that the genes responsible
for these two mutations are 8 m.u. apart. The geneticist mixes phages with genotype c+ m+ and genotype cm- and uses the mixture to infect bacterial cells. She collects the progeny phages and cultures a sample of
them on plated bacteria. A total of 1000 plaques are observed. What numbers of the different types of
plaques (c+ m+, c- m-, c+ m-, c- m+) should she expect to see?
4.
E. coli cells are simultaneously infected with two strains of a phage–– one has the mutant genotype for all
three genes (h st c) and the other has the wild type genotype for all three genes (h+ st+ c+). Progeny phages
are collected from the lysed cells and are plated on bacteria. The numbers of different progeny phages are
given here.
a. ) Determine the order of the three genes on the phage chromosome.
Progeny phage genotype
Number of plaques
h+ c+ st+
321
h c st
338
h+ c st
26
h c+ st+
30
h+ c st+
106
h c+ st
110
h+ c+ st
5
h c st+
6
genes.
5.
b.) Determine the map distance between the
Two mutations that affect plaque morphology in phages (a- and b-) have been isolated. Phages carrying
both mutations (a- and b-) are mixed with wild-type phages (a+ and b+) and added to a culture of bacterial
cells. Subsequent to infection and lysis, samples of the phage lysate are collected and cultured on bacterial
cells. The following numbers of plaques are observed:
Plaque phenotype
Number
a+ b+
2043
a+ b-
320
a- b+
357
a- b-
2134
What is the frequency of recombination between the a and b
genes?
6. A geneticist isolates two bacteriophage r mutants (r13
and r2) that cause rapid lysis. He carries out the following crosses and counts the number of plaques listed
here:
Genotype of Parental Phage
h+ r13- x h- r13+
h+ r2-
x
h- r2+
Progeny
Number
h+ r13+
1
h- r13+
104
h+ r13-
110
h- r13-
2
h+ r2+
6
h- r2+
86
h+ r2-
81
h- r27
a.) Calculate the recombination frequencies between r2 and h and between r13 and h.
b.) Draw all possible linage maps for these three genes.