Biology Reference
In-Depth Information
74
For a given experimentally measured co-transduction frequency, the straight
line in Fig. 3-2 and the curve in Fig. 3-5 give very different distances
between the two genetic markers. In the case of the experiment mentioned
before, we have:
D AB = 0.50 min ,
D BC = 0.34 min ,
and
D AC = 0.85 min .
Therefore, the sum of D AB and D BC is 0.84 min close to 0.85 min, D AC .
The estimated distances between genetic markers using the biological
relevant curve (Fig. 3-5) are much smaller than those estimated by the
straight line relation (Fig. 3-2). With this mathematical modeling, three-
point analysis can give consistent and accurate distances between the three
consecutive genetic markers as discussed below.
THREE-POINT ANALYSIS
Transduction experiments were performed for numerous genetic markers of
E. coli , some involve three nearby consecutive ones. These experiments
have been referred to as three-point analysis. Let us assume that A, B and C
are the three nutrient supplements required for the growth for the recipient
strain which is thus denoted as A-B-C-. On the other hand, the donor
strain does not require these for growth, so that it is designated as A+B+C+.
In a typical experiment, P1-phage is first grown with the donor strain and
then harvested. After mixing with the recipient strain, they are then plated
out on plates with supplements B and C, C and A, or A and B, to select for
A+, B+ and C+ transductants respectively. Streptomycin can be used to
eliminate the background growth of the donor strain as in a conjugation
experiment.
After a day or two, transductants will form colonies on these three plates.
Each colony is then picked by sterile tooth-picks and patched onto plates
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