`
`
`
`APPENDIX B
`
`
`
`eyatrs
`sAFATNSNS
`
`Consider two DNAtargets T1 and T2 corresponding to two dyes FAM andVIC, respectively
`Let T1 and T2 be always on separate DNAfragments. Let the number of DNA fragments
`with T1 and T2 targets be M1 and M2 respectively.
`
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`Let the counts of FAM and VIC positive partitions be N1 and N2, respectively. Note that N1
`and N2 will be smaller than M1 and M2,respectively, as there can be multiple DNA
`fragments in a partition. Let the total number of partitions be N. We will refer to digital
`PCR partitions simply as partitions. In this case, we can expectto see the following table of
`countsof partitions.
`
`S
`
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`
`| VIC Negative
`FAM Positive
`N1.(N-N2)/N
`FAM Negative
`
`
`
`N1 .N2/N
`
`N1
`
`N -N1).(N-N2)/N_|(N-N1).N2/N oo
`[No
`
`If we denote the probability of seeing a partition to be FAM positive as p1=N1/N, and of
`seeing a partition to be VIC positive as p2 = N2/N, then the corresponding probability table
`is:
`
`|CIC Negaattive Probabili
`
`
`FAM Positive
`
`
`FAM Negative
`L-p1).(1-p2
`iap! p2
`
`Probabili
`
`1-p2
`
`In this case, we can say that 100% fragmentation exists.
`
`Appendix B
`
`
`
`We can compute the number of T1 and T2 molecules, M1 and M2, respectively as follows
`M1 =-N log(1 - p1)
`M2 = -N log(1 - p2)
`
`(Given N digital partitions in which P are positive, the numberof molecules is
`- N log (1 -P/N).)
`
`
`
`Nowconsider the other extreme. Both the targets T1 and T2 are on the same DNA fragment
`always. Theyare linked, perhaps because their loci are quite close to each other on the
`same part of a chromosome, andrestriction enzymedid not cut these into separate parts
`Therefore N1 = N2.
`
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`
`
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`
`FAM Negative
`
`Probabili
`
`a Negative
`a p1
`
`1-p1
`
`Probabili
`
`In this case, we can say that 0% fragmentation exists
`
`Wecan compute the number of T1 and T2 molecules as follows, where p1=N1/N
`M1 =-N log(1 - p1)
`M2 = -N log(1 - p1)
`
`Appendix B
`
`
`
`
`
`In intermediate situation, when on the targets are together on the some fragments,but also
`happen to be on separate fragments, then wehave partial fragmentation.
`
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`
`Suppose we have M3 molecules of linked T1 and T2 fragments, M1 molecules of separate
`T1 fragments, and M2 molecules of separate T2 fragments.
`
`Wemakea table of counts ofpartitions.
`
`|CCC VIC Negative
`FAM Positive
`FAM Negative
`
`
`
`Problem Statement
`
`How can wefind number of molecules M1, M2 and M3, and therebygetting extent of
`fragmentation? For example if M1 = M2 = M3, then we would saythat there is 50%
`fragmentation, as 50% of linked molecules got fragmented into separate fragments and
`50% remainedintact.
`
`
`
`Suppose wehave a solution to the above problem. Then we have anotherinteresting
`application of this solution. Using this algorithm and by using FAM probe fora target T1,
`VIC probe for target T2, and both FAM andVIC probes placed close to each other for third
`target T3, we can achieve multiplexing of 3 targets by using 2 colors.
`
`Basically, we geta third color for “free” using the abovealgorithm.
`
`Nowconsider the case if there are 3 dyes. Thus, wewill have 2x2x2 table of 8 observed
`counts.
`
`Appendix B
`
`
`
`There are 7 different kinds of targets: T1, T2, T3, T12, T23, T13, T123. Here, for example,
`T12 means target in which weplace Dye 1 and Dye 2 probes nextto each other on the
`amplicon region, and T123, meanstarget in which putall the three dyes together on the
`same amplicon,andlikewise for others.
`
`If we have 4 dyes, then we have 24 = 16 counts, and we can now multiplex quantitation of
`2* -1 = 15 target genes. In general, with n colors, we have 2" observed counts and we can
`have 2"-1 targets.
`
`b
`£3
`at
`S
`atSeetad of
`SYSS ANG
`
`Suppose weare given the following counts:
`
`Total|N= N2
`
`| VIC Negative
`FAM Positive NorNIEND
`
`FAM Negative
`
`Consider the following three cases:
`1. Weturn off VIC, as if VIC can not be seen atall.
`2. We turn off FAM, as if FAM can not be seen atall.
`3. We consider both FAM and VIC asif they are really 1 color.
`
`Wewill have the three observations:
`1. Turning off VIC: We will be able to see T1 or T12, together andindistinguishably, as
`if there were one target. It gives the total numberof molecules of T1 and T12, asif
`there were one target species.
`2. Turning offFAM: We will be able to count T2 or T12, indistinguishably,as if there
`were one target. It gives the total numberof molecules of T2 and T12, as if there
`were one target species.
`3. Considering both FAM and VICindistinguishably: We will be able to count T1, T2 or
`T12, indistinguishably.It gives the total numberof molecules of T1, T2 and T12, as if
`there were one target species.
`
`This allows us to step 3 equations in 3 unknowns. We can showthese three cases in the
`form ofa table.
`
`Invisible|Distinct Indistinct|Target Positive Count|Molecules
`
`
`Dyes
`Dyes
`Dyes
`Detected
`
`
`
`aaN1/N
`aaN2/N
`
`4
`
`Appendix B
`
`
`
`Visible Invisible|Distinct Indistinct|Target Positive Count|Molecules
`
`
`
`Dyes
`Dyes
`Dyes
`Dyes
`
`Detected FAM,VIC
`
`{FAM, {T1,T2,T12}|NO1+N10+N11|-log(1 -
`
`VIC}
`(NO1+N10
`
`The 3 linear equations in 3 unknowns M1, M2 and M12 are:
`
`101
`tit
`
`011
`
`1
`12
`
`2 =
`
`=
`
`|
`
`— log 1-—
`
`|
`*
`— log 1-—
`|
`9
`01+ 10+ |
`|- log(1 - —————}
`
`Wesolve the above equationsto get values of M1, M2 and M12.
`
`Wecan then computethe extentof fragmentation in % as follows:
`M = (M1 + M2)/2
`F = M/(M + M12) * 100
`
`8
`A
`Aig
`
`Now wewrite downthesteps of the algorithm clearly.
`
`
`
`ieee TRV ¥INPU
`
`[VIC Negative
`FAMPositive
`
`[N12
`
`N2
`
`
` FAMNegative N21 N22 ¥Aa___
`
`
`N-N2
`
`Step 1. Compute the three entities:
`Mioriz = -N . log(1 - N1/N)
`Moor12 = - N. log(1 - N2/N)
`Mior2or12 =- N. log(1 -(N01+N10+N11)/N)
`
`5
`
`Appendix B
`
`
`
`Step 2. Solve the following linear equations:
`
`101
`
`tid
`
`1
`
`12
`
`[
`
`1
`
`— log 1-—
`2
`
`|
`
`01+ 10+ 11
`— log(1 —- —————_)
`
`Step 3. Compute extent of fragmentation.
`M = (M1 + M2)/2
`F = M/(M + M12) * 100
`
`Step 4. Compute confidence intervals based on the concentration and expected number of
`positive counts. To computeconfidence interval of F, we notethat it is ratio of two random
`variables. Then we apply techniques to estimate confidence interval of ratio of two random
`variables for F.
`
`Now wepresent analternative solution to the problem of partial fragmentation phrased in
`termsof optimization of an objective criterion. First let us make the following table.
`Depending upon what type of molecules wehavein a partition we will have corresponding
`FAM andVIC colors of the partition.
`
`Table mapping molecules into partition color
`
`oFNeg Neg
`jooegPos
`aCPosNeg
`
`
`
`Suppose we make a “guess” of M1, M2 an M12. Wecan compute the probabilities ofa
`partition having T1, T2 or T12 target using inverse equations:
`p12 =1- exp(-M12/N)
`p1=1-exp(-M1/N)
`p2 =1-exp(-M2/N)
`
`6
`
`Appendix B
`
`
`
`From these probabilities we can compute the predicted countsas follows.
`
`|i VIC Negative
`
`FAM Positive|p1(1-p2)(1-p12)N (1 - (sum of other 3 cells
`
`in this table))N FAM Negative|(1-p1)(1-p2)(1-p12)N
`
`(1-p1)p2(1-p12)N
`
`The probabilities above can be filled using the table shown above which maps presence of
`molecules into partition colors.
`
`If our “guess'is really correct, then the predicted counts will “match” closely with our
`expected counts. Thus an optimization algorithm underthe above objective criterion that
`needs to be minimized could also be used to solve the problem.
`
`M1, M2, M12 = best guess= least deviation of predicted counts and actual counts
`
`Wecan then computethe extent of fragmentation in % as follows:
`M = (M1 + M2)/2
`F = M/(M + M12) * 100
`
`rs
`y 2
`LY F
`So ap
`3 ay ye
`SAARATAANA
`WAG § LArSess
`
`To solve the problem for greater number of dyes, we need more equationsas there are
`more unknowns. For 3 dyes and 7 targets, we need 7 equationsto find the concentration of
`these 7 targets.
`
`Wehavethe following table with 2° = 8 rowsof counts of partitions depending upon which
`dyes are positive.
`
`Denote the three dyes by D1, D2 and D3.
`
`Presence ofcolor ina pso CountofPartitions
`Rego
`
`
`
`Neg
`
`Neg
`
`NO10
`
`N100
`NOO1
`NO11
`
`N101
`
`7
`
`Appendix B
`
`
`
`Consider the following table.
`
`Detected
`Dyes
`Dyes
`Dyes
`Dyes
`
`
`D1,D2,D3
`T12, T13, T23,
`
`- {D1,D2,D3}|{T1,T2,T3, C1 =N -NO000
`
`
`
`D1
`
`D2, D3
`
`D1, D3
`
`D1, D2
`
`{T1,T12,T13,
`T123}
`
`{T2,T12,T23,
`T123}
`
`{T3,T13,T23,
`T123}
`
`D3
`
`D1,D2
`
`{T1,T13}
`
`D2
`
`D1,D3
`
`{T1,T12}
`
`D1
`
`D2,D3
`
`{T2, T12}
`
`C2 =
`N100+N101+N110+
`N111
`C3 =
`N0O10+N011+N110+
`N111
`C4 =
`N0O01+N011+N101+
`N111
`Compute
`concentration
`Mior13 by solving 2
`dye problem*
`Compute
`concentration
`Mior12 by solving 2
`dye problem*
`Compute
`concentration
`Moaor12 by solving 2
`dye problem*
`
`*Note that for row 5, we could have also detected {T2,T23} or {T12, T123}, and for row 6,
`{T3, T23}, and for row 7, {T3, T13} and {T23, T123}. This choice does not matter andall
`lead to same results.
`
`We make 3 recursivecalls, in rows 5, 6 and 7.
`
`For example, in row 5, we are really solving 2 dyes, D1 and D2, case with 3 targets: {T1,
`T13} as one target, {T2, T23} as second target, and {T12, T123} as third linked target.
`
`Similarly, in rows 6 and 7, we makerecursivecalls to solve simpler problem of 2 dyes and 3
`targets.
`
`8
`
`Appendix B
`
`
`
`The system of equation lookslike as follows:
`
`1
`log 1-—
`
`11111147
`
`/1001101||
`}0101011]|
`0010111]|
`1000100]|
`1001000||
`
`0101000)L
`
`1
`
`|
`2 |
`3
`|
`12 =|
`13
`23
`
`123
`
`2
`
`— log 1-—
`|
`I 3 |
`yo og 1 |
`4 |
`|
`j- log 1-—|
`
`|
`
`|
`
`SA 8Aneantin
`
`
`
`Now wegivethe steps to generalize the algorithm to arbitrary number of dyes. This isa
`recursive algorithm.Since we have a solution for the case when R = 2, we cansolvefor any
`number of R through recursion.
`
`For R dyes, we are given a table of counts of partitions which has 28 rows,for all possible
`combinationsof presence or absenceof colorsin a partition.
`
`
`
`oy
`STEP 1. Set up a system of 28-1 linear equations. To obtain these equations consider
`different ways of making somecolors invisible. Also consider the case when all colors are
`indistinguishable, whichgivesthefirst row. It can be shownthat we can obtain 2 - 1
`equations in 28 - 1 target concentrations (unknowns). When we makecertain colors
`invisible, then we reduce the problem to a case with fewer colors, which can be solved
`recursively, all the way downto case when there are 2 dyes and 3 targets.
`
`STEP2. Solve the equations.
`
`STEP 3. Compute confidence intervals based on the concentration and expected number of
`positive counts.
`
`ns
`vyOUTPUT:
`At
`Se
`pond
`
`Concentrations of 28- 1 targets along with confidenceintervals.
`
`9
`
`Appendix B
`
`