EXAMINATION VI

UNDERLINE ALL THE ALTERNATIVES WHICH ARE CORRECT,

272

In replica plating

a. separate colonies, one should make the
first copy on the same medium as the mas-
ter plate.

b. continuous colonies, the first copy can
usually be used in place of the master
plate.

ce. continuous colonies, it is necessary to
label the positions the plates have taken
on the velvet.

d. separate clones, spontaneous mutations
within a clone can be disregarded.

e. one can transfer phage as well as bacteria,

DNA

a. is sometimes one-stranded, like RNA
must be,

b. synthesized in vitro has many of the pro-
perties of the primer DNA but is not
biologically active.

c. is probably self-replicating in many
places in the universe at the present time.

d. is itself a linear polymer.

€. can normally occur uncombined with other
substances.

Escherichia coli strain K-12

a, usually reproduces sexually, each organ~
ism being one of three mating types.

b. produces one clone from a single indivi-
dual.

c. is attacked by more than one type of virus.

d. is best isolated by the use of the replica-
plating technique.

e. was discovered by Lederberg and Tatum
in 1946.

The fertilization process in bacteria always
a. produces recombination.

b. involves two whole cells,
c. involves two different mating types, of

which one must be F-.
d. involves two of the nuclei in an E. coli
cell. .
e. includes transfer of DNA, but excludes
transfer of RNA.

Salmonella typhimurium

a, undergoes sexual recombination as does
its relative E. coli.

b. undergoes transduction via phage P22.

c. is attacked by T4, which can carry more
than one bacterial marker at a time.

d. has n'its, each of which is capable of be-
ing carried by a transducing phage,

e. has some of its genes arranged in the
same order as the chemical processes
occur which these genes control.

By becoming infected, a bacterium

a. can change its mating type.

b. can shift its manufacture of DNA and pro~
tein from one type to another.

c. runs the risk of lysis because all the viru-
lent virus usually enters the cell.

d. may become a prototroph even if it was
previously auxotrophic.

e. may give rise to progeny which have lost
a specific allele present before infection.

Smaller plant and animal viruses

a, are always composed of RNA which is
usually single-stranded.

b. may require several hours after infection
to produce daughter particles.

c. which specify only a few proteins may not
be so virulent for this reason.

d. do not have the protein tail so character-
istic of bacteriophage.

e. are often difficult to assay because of
their size.
10,

11.

Mixed infections involving different strains
of a virus

a. do not occur with tobacco mosaic virus al-
though they do occur with influenza virus.

b. can give rise to phenotypic mixing and
heterozygosis, but not to true genetic re-
combination.

ce. occur with vaccinia virus, leading to re-
combination of its genes.

d. do not occur for viruses containing RNA.

e. do not occur if the technique of limit-dilu- 12.

tion is employed.

The number of n'its in a genome

a, is greater for free-living than for parasi-
tic or symbiotic organisms.

b. can give an estimate of the number of

genes therein, simply by dividing by
2x 10°,

c. is a good estimate of the total number of
crossover sites.

d. is approximately equal to the number of
mutational sites.

e. refers to the number of linearly arranged

organic bases in a set of genes, whether 13.

in RNA or DNA.

If a clone is streaked across agar including
a section containing sufficient streptomycin,

a. no appreciable growth will occur on the
plate if the clone was prototrophic and the
medium minimal.

b. its growth, everywhere but on the strepto-
mycin, shows it is streptomycin-resis-
tant.

c. you can be sure no sexual processes are 14,

taking place to confuse the results.

d. mutation to streptomycin-resistance would
be indicated if a very small amount of
growth occurred in the streptomycin-con-
taining region, but much growth occurred
in the drug-free region.

e. uniform growth along the streak indicates
the clone is streptomycin-resistant, al-
though it may be auxotrophic.

Genetic recombination in bacteria 15.

a. cannot be visualized as an asexual pro-

cess except through the use of the electron
microscope.

b. proved that gene exchange must have oc-
curred by a sexual process.

ec. can only occur between auxotrophs for
different nutritional requirements.

d. may be the cause of new virulence.

e. can be induced by man in a way that ordi-
narily does not occur in nature.

The fluctuation test of Luria and Delbrtick

a. showed that the medium used did not select
mutants preferentially.

b. gave a normal distribution for the number
of mutants in different samples tested.

c. was the first demonstration with bacteria
of the occurrence of mutations without re-
gard to the specific medium upon which
the mutants are detected.

d, showed that mutations can occur any time
in clonal growth.

e. gave results easily reproduced by using
techniques of replica plating.

Purified nucleic acids can act genetically

a. when introduced into tobacco, mammalian,
or bacterial cells.

b. when they are either RNA or DNA.

c. when these have been obtained from organ-
isms other than viruses.

d. and when taken from virus can produce
complete daughter virus particles.

e. even after they are surrounded by a pro-
tein coat unlike their original one.

F- cells of E. coli

a. cannot contribute any of their hereditary
material to other cells.

b. can become Hfr cells only by first becom-
ing Ft,

c. are sites for synapsis and crossingover.

can be heterogenotes or heterozygotes.

e. cannot be lysed by lambda unless exposed
to ultraviolet light.

a

Bacteriophage

a. does not contain phosphorous in its protein.

273
b. may be infective even when its coat is 16. Ther region of T4
punctured or removed.

c. contains no RNA in its coat, tail, or spiral a. contains 1% of the total n'its present in
fiber. that phage.

d. is not infective when multiplying. b. is composed of about 100 cistrons, as de-

e. could not be detected if it multiplied slower tected from spontaneous mutation experi-
than its host. ments.

c. is especially suitable for studies of genetic
recombination rates.

d. cannot lyse strain K-12 when it is mutant.

e. can only demonstrate recombination when
hosts are mixedly-infected.

17. Whenever the research of the workers listed in column A can be associated with an item in column
B place the appropriate number in the space provided.

 

 

 

 

 

 

 

 

A. B.
1. Sinton
2. Benzer
3. Hershey and Chase Plant virus
4, Schramm Origin of life
5. Lederberg and Tatum Protein
6. Demerec Salmonella
7. Fraenkel-Conrat Phage
8. Luria and Delbrtick RNA
9. Wollman and Jacob F* mating type
10, Zinder DNA
11. Levinthal
12. Miller and Urey
13. Burnet

274