Discussion
The Hfr strain of Escherichia coli is one in which
Answer: B
Correct answer: the F plasmid has integrated into the bacterial chromosome
An Hfr cell - high frequency of recombination - is one in which the F plasmid has integrated into the chromosome by homologous recombination at an insertion sequence. The consequence is that conjugation now transfers chromosomal genes. Transfer begins at the point of integration and proceeds linearly, so genes nearest that point enter the recipient first. Because the mating pair almost always separates before the whole chromosome has passed, the recipient usually receives only a portion, and rarely the F plasmid itself - which is why an Hfr cross seldom converts the recipient to a donor, unlike an F+ cross. The name records the high rate of chromosomal recombinants such crosses produce. Its experimental value is interrupted mating: breaking the mating at intervals and testing which markers have arrived gives their order and spacing along the chromosome, measured in minutes of transfer time. The whole E. coli chromosome takes about 100 minutes.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development