Bacterial Mapping Problem A cross is made between two E. coli strains: Hfr: a+b+
ID: 18878 • Letter: B
Question
Bacterial Mapping Problem A cross is made between two E. coli strains: Hfr: a+b+c+ (a, b, and c are nutritional requirements) F-: a- b- c- Interrupted-mating studies show that a+ enters the recipient last, so a+ recombinants are selected on a medium containing b and c only. The selected cells are a+ recombinants (can grow without a). The a+ recombinants are tested for the presence of b+ and c+. The following numbers of colonies are found for each genotype. What is the gene order ? Since *a* enters last the gene order is either (1) a-b-c OR (2) a-c-bExplanation / Answer
The answer is (2) a-c-b
This is because a double recombinant occurs in least frequency (because it requires two crossover events rather than one) and when a double recombinant occurs, the net result is the middle gene "flipping over". Hence, from the frequencies, we can see that the a+b+c- recombinant occurs in least frequency (0) and thus gene c flipped as a result of a double crossover between a and c as well as c and b.
Related Questions
Hire Me For All Your Tutoring Needs
Integrity-first tutoring: clear explanations, guidance, and feedback.
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.