Chapter 7-- Linkage and Mapping in Prokaryotes

a. resistant to penicillin?

trp+ pyrC+ purB+86trp+ pyrC+ purB-4trp+ pyrC- purB+67

single transformants recombination rate (m.u.) = ----------------------------- x 100 total number of transformants 67 + 4 recombination rate = ------------ x 100 = 45 m.u. 67 + 4 + 86

number withSimilarly, the cotransfer index fortrp+andpurB+cotransfer index (r) = --------------------------------------- total number of tranformants 67 + 86 cotransfer index = --------- = 0.89 171

number withAs the contransfer index fortrp+andpyrC+cotransfer index (r) = --------------------------------------- total number of tranformants 86 + 4 cotransfer index = --------- = 0.53 171

Approximate Time of Entry ---------------------------------- Donor Loci Hfr P4X Hfr KL98 Hfr Ra-2 ----------------------------------------------------- gal+ 11 67 70 thr+ 94 50 87 xyl+ 73 29 8 lac+ 2 58 79 his+ 38 94 43 ilv+ 77 33 4 argG+ 62 18 19 -----------------------------------------------------How many different petri plates and selective media are needed?

lac(2)--gal(11)--his(38)--argG(62)--xyl(73)--ilv(77)--thr(94)

For Hfr KL98, the order is:

agrG(18)--xyl(29)--ilv(33)--thr(50)--lac(58)--gal(67)--his(94)

For Hfr Ra-2, the order is:

ilv(4)--xyl(8)--argG(19)--his(43)--gal(70)--lac(79)--thr(87)

Notice that the direction of transfer for Ra-2 is backwards from that of the other two strains. Notice also that the time of transfer between the loci is constant from one Hfr strain to the next. For example, between lac(2) and gal(11) is 9 minutes for Hfr P4X and the time of transfer between gal(70) and lac(79) for Hfr Ra-2 is also 9 minutes, though the direction of transfer is opposite. The best way to show the map is with a diagram of the bacterial chromosome. We will arbitrarily assign the

a+ b- c-21a+ b- c+69a+ b+ c-3a+ b+ c+7

number withSimilarly, the cotransfer index fora+andb+cotransfer index (r) = --------------------------------------- total number of tranformants 69 + 7 cotransfer index = --------- = 0.76 100

number withAs the contransfer index fora+andb+cotransfer index (r) = --------------------------------------- total number of tranformants 7 + 3 cotransfer index = --------- = 0.10 100

The conjugant in highest frequency represents the locus that was transfered first, the conjugant in second highest frequency represents the locus transferred second. Thus if we simply rank the conjugants from most frequent to least frequent, the loci will be in that order on the bacterial chromosome from first to last. Note that no colonies that were his+ were isolated, which means that it would be transferred last of these four and that it is further along the bacterial chromosome that 25 minutes. The order of the loci is thr -- leu -- pro -- his.Genotype number of colonieshis+0leu+12thr+27pro+6

a. What genotype will grow on this medium?

lys+ val+ his+ 0 lys+ val+ his- 75 lys+ val- his+ 6From the table, we can see that

val+ his+ lys+ 0 val+ his- lys+ 37 val+ his+ lys- 3 val+ his- lys- 10

Last updated on 22 August 1996.