specify number of reactions to setup on last step if replicates are requested

[kalekundert]

Here's a (long) example from a protocol I just did:

14. Setup 96 PCR reactions:

    - Use the following combinations of reagents:

      template DNA                     forward primer  reverse primer
      ───────────────────────────────────────────────────────────────
      sz224, SuperScript IV, +RT       s1              s2
      sz224, SuperScript IV, +RT       s3              s5
      sz224, SuperScript IV, −RT       s1              s2
      sz224, SuperScript IV, −RT       s3              s5
      sz228, SuperScript IV, +RT       s1              s2
      sz228, SuperScript IV, +RT       s3              s5
      sz228, SuperScript IV, −RT       s1              s2
      sz228, SuperScript IV, −RT       s3              s5
      sz224, SuperScript IV VILO, +RT  s1              s2
      sz224, SuperScript IV VILO, +RT  s3              s5
      sz224, SuperScript IV VILO, −RT  s1              s2
      sz224, SuperScript IV VILO, −RT  s3              s5
      sz228, SuperScript IV VILO, +RT  s1              s2
      sz228, SuperScript IV VILO, +RT  s3              s5
      sz228, SuperScript IV VILO, −RT  s1              s2
      sz228, SuperScript IV VILO, −RT  s3              s5
      sz224, ProtoScript II, +RT       s1              s2
      sz224, ProtoScript II, +RT       s3              s5
      sz224, ProtoScript II, −RT       s1              s2
      sz224, ProtoScript II, −RT       s3              s5
      sz228, ProtoScript II, +RT       s1              s2
      sz228, ProtoScript II, +RT       s3              s5
      sz228, ProtoScript II, −RT       s1              s2
      sz228, ProtoScript II, −RT       s3              s5
      sz224, AMV, +RT                  s1              s2
      sz224, AMV, +RT                  s3              s5
      sz224, AMV, −RT                  s1              s2
      sz224, AMV, −RT                  s3              s5
      sz228, AMV, +RT                  s1              s2
      sz228, AMV, +RT                  s3              s5
      sz228, AMV, −RT                  s1              s2
      sz228, AMV, −RT                  s3              s5

    - Make 2 primer mixes:

      Reagent          Stock   Volume   ≈173.7x
      ─────────────────────────────────────────
      forward primer  100 µM  0.05 µL   7.82 µL
      reverse primer  100 µM  0.05 µL   7.82 µL
      ─────────────────────────────────────────
                              0.09 µL  15.63 µL

    - Make polymerase mix:

      Reagent          Stock    Volume     ≈137.7x
      ────────────────────────────────────────────
      water                    8.01 µL  1102.75 µL
      Luna master mix     2x   9.00 µL  1239.04 µL
      ────────────────────────────────────────────
                              17.01 µL     2.34 mL

    - Make 2 master mixes:

      Reagent           Volume      ≈62.6x
      ────────────────────────────────────
      primer mix       0.09 µL     5.63 µL
      polymerase mix  17.01 µL  1064.45 µL
      ────────────────────────────────────
                      17.10 µL  1070.08 µL

    - Setup the reactions:

      Reagent            Stock    Volume     ≈3.6x
      ────────────────────────────────────────────
      master mix                17.10 µL  60.80 µL
      template DNA  <100 ng/µL   0.90 µL   3.20 µL
      ────────────────────────────────────────────
                                18.00 µL  64.00 µL

    - Split into 3 identical 18.00 µL reactions.

    - Use any extra master mix as a negative control.

I'm going to setup 96/3 = 32 master mix + DNA reactions, but the protocol doesn't say this. With no replicates this makes sense, because the information would be redundant, but with replicates it's not. And even without replicates, being redundant may be useful for long protocols like this one...