Each phage particle will package about 1/50 of the E.coli chromosome.By combining probabilities we see that about 1/15,000 phage will carry a particular E.coli gene. A basic transduction experiment to measure the linkage between markers A and B is done as follows: (1)Grow P1 on A+B+ (2)Infect A B (3)Select for A+and then screen for B+ The idea is that we are looking for the rare cases where some chromosomal DNA carrying gene A is moved into the recipient.To find these recombinants,we select for A+.Then we screen for B+to see how often gene B comes along with gene A. 4+ B+ A B The measured frequency of cotransduction of B with A gives a measure of distance according to the following rules: If distance between A and B is greater than one headfull(105 bp)then there will be no cotransduction. If A and B are very close together then there will be 100%cotransduction. Cotransduction frequency is an inverse measure of distance. 100 % cotransduction one headfull ↓ 0 distance between markers The experiment just described is the bacterial equivalent of a 2-factor cross and will give us relative distances between genes.Each phage particle will package about 1/50 of the E. coli chromosome. By combining probabilities we see that about 1/15,000 phage will carry a particular E. coli gene. A basic transduction experiment to measure the linkage between markers A and B is done as follows: (1) Grow P1 on A+B+ (2) Infect A–B– (3) Select for A+ and then screen for B+ The idea is that we are looking for the rare cases where some chromosomal DNA carrying gene A is moved into the recipient. To find these recombinants, we select for A+. Then we screen for B+ to see how often gene B comes along with gene A. A- B￾A+ B+ The measured frequency of cotransduction of B with A gives a measure of distance according to the following rules: • If distance between A and B is greater than one headfull (105 bp) then there will be no cotransduction. • If A and B are very close together then there will be 100% cotransduction. • Cotransduction frequency is an inverse measure of distance. 100 % cotransduction 0 distance between markers one headfull The experiment just described is the bacterial equivalent of a 2-factor cross and will give us relative distances between genes