An Hfr strain is used to map three genes in an interrupted mating experiment. The cross is Hfr/a+b+c+ rif x F-a-b-c- rifr (note that rifr is resistance to the antibiotic rifampicin). The a+ gene is required for the biosynthesis of nutrient A, the b+ gene for nutrient B, and the c+ gene for nutrient C. The cross is initiated at time=0. At various times, the mating mixture is plated out on three different types of medium. Each plate contains minimal medium (MM) plus rifampicin, plus specific supplements that are listed in the table below. The results for each time interval are shown as the number of colonies growing on each plate.An Hfr strain is used to map three genes in an interrupted mating experiment. The cross is Hfr/a+b+c+ rif x F-a-b-c- rifr (note that rifr is resistance to the antibiotic rifampicin). The a+ gene is required for the biosynthesis of nutrient A, the b+ gene for nutrient B, and the c+ gene for nutrient C. The cross is initiated at time=0. At various times, the mating mixture is plated out on three different types of medium. Each plate contains minimal medium (MM) plus rifampicin, plus specific supplements that are listed in the table below. The results for each time interval are shown as the number of colonies growing on each plate. Time of Interruption 5 min. 10 min. 15 min. 20 min. Nutrients A and B 0 0 4 21 Nutrients B and C 0 5 23 40 Nutrients A and C 4 25 60 82 a. What is the purpose of rifampicin in the experiment? Why is rifampicin included in all three types of medium? b. What is the gene order of transfer for the three genes, from first to last? How can you tell? c. Can you determine the approximate distance between the three loci? What are the units of such distance measurements? d. Can the location of the rif gene be determined in this experiment? Why or why not?
Genetic Recombination
Recombination is crucial to this process because it allows genes to be reassorted into diverse combinations. Genetic recombination is the process of combining genetic components from two different origins into a single unit. In prokaryotes, genetic recombination takes place by the unilateral transfer of deoxyribonucleic acid. It includes transduction, transformation, and conjugation. The genetic exchange occurring between homologous deoxyribonucleic acid sequences (DNA) from two different sources is termed general recombination. For this to happen, an identical sequence of the two recombining molecules is required. The process of genetic exchange which occurs in eukaryotes during sexual reproduction such as meiosis is an example of this type of genetic recombination.
Microbial Genetics
Genes are the functional units of heredity. They transfer characteristic information from parents to the offspring.
An Hfr strain is used to map three genes in an interrupted mating experiment. The cross is Hfr/a+b+c+ rif x F-a-b-c- rifr (note that rifr is resistance to the antibiotic rifampicin). The a+ gene is required for the biosynthesis of nutrient A, the b+ gene for nutrient B, and the c+ gene for nutrient C. The cross is initiated at time=0. At various times, the mating mixture is plated out on three different types of medium. Each plate contains minimal medium (MM) plus rifampicin, plus specific supplements that are listed in the table below. The results for each time interval are shown as the number of colonies growing on each plate.An Hfr strain is used to map three genes in an interrupted mating experiment. The cross is Hfr/a+b+c+ rif x F-a-b-c- rifr (note that rifr is resistance to the antibiotic rifampicin). The a+ gene is required for the biosynthesis of nutrient A, the b+ gene for nutrient B, and the c+ gene for nutrient C. The cross is initiated at time=0. At various times, the mating mixture is plated out on three different types of medium. Each plate contains minimal medium (MM) plus rifampicin, plus specific supplements that are listed in the table below. The results for each time interval are shown as the number of colonies growing on each plate.
Time of Interruption
5 min. 10 min. 15 min. 20 min.
Nutrients A and B 0 0 4 21
Nutrients B and C 0 5 23 40
Nutrients A and C 4 25 60 82
a. What is the purpose of rifampicin in the experiment? Why is rifampicin included in all three types of medium?
b. What is the gene order of transfer for the three genes, from first to last? How can you tell?
c. Can you determine the approximate distance between the three loci? What are the units of such distance measurements?
d. Can the location of the rif gene be determined in this experiment? Why or why not?
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