Using bacteriophage P22, you performed a threefactor cross in Salmonella typhimurium. The crosswas between an Arg− Leu− His− recipient bacteriumand bacteriophage P22, which was grown on an Arg+Leu+ and His+ strain. You selected for 1000 Arg+transductants and tested them on several selective media by replica plating. You obtained the followingresults:Arg+ Leu− His− 585Arg+ Leu− His+ 300Arg+ Leu+ His+ 114Arg+ Leu+ His− 1a. What are the cotransduction frequencies of argwith either his or leu?b. Is arg closer to his than it is to leu, or is arg closerto leu than it is to his? What are the relative mapdistances?c. Why can you not obtain an accurate cotransductionfrequency for his and leu from the data provided?d. What is the order of the three markers?e. Draw the crossovers that would produce the classwith only one transductant.f. Estimate the proportion of the 4.9 Mb S. typhimuriumgenome that contains these three genes. Assume thatbacteriophage P22 can package the same amountof DNA as the E. coli virus P1.
Bacterial Genomics
The study of the morphological, physiological, and evolutionary aspects of the bacterial genome is referred to as bacterial genomics. This subdisciplinary field aids in understanding how genes are assembled into genomes. Further, bacterial or microbial genomics has helped researchers in understanding the pathogenicity of bacteria and other microbes.
Transformation Experiment in Bacteria
In the discovery of genetic material, the experiment conducted by Frederick Griffith on Streptococcus pneumonia proved to be a stepping stone.
Plasmids and Vectors
The DNA molecule that exists in a circular shape and is smaller in size which is capable of its replication is called Plasmids. In other words, it is called extra-chromosomal plasmid DNA. Vectors are the molecule which is capable of carrying genetic material which can be transferred into another cell and further carry out replication and expression. Plasmids can act as vectors.
Using bacteriophage P22, you performed a threefactor cross in Salmonella typhimurium. The cross
was between an Arg− Leu− His− recipient bacterium
and bacteriophage P22, which was grown on an Arg+
Leu+ and His+ strain. You selected for 1000 Arg+
transductants and tested them on several selective media by replica plating. You obtained the following
results:
Arg+ Leu− His− 585
Arg+ Leu− His+ 300
Arg+ Leu+ His+ 114
Arg+ Leu+ His− 1a. What are the cotransduction frequencies of arg
with either his or leu?
b. Is arg closer to his than it is to leu, or is arg closer
to leu than it is to his? What are the relative map
distances?
c. Why can you not obtain an accurate cotransduction
frequency for his and leu from the data provided?
d. What is the order of the three markers?
e. Draw the crossovers that would produce the class
with only one transductant.
f. Estimate the proportion of the 4.9 Mb S. typhimurium
genome that contains these three genes. Assume that
bacteriophage P22 can package the same amount
of DNA as the E. coli virus P1.
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