Single cell Drop-Seq question

Question

[landscape95]

Hello everyone, I am reading about drop-seq in paper "Single-cell RNA sequencing for the study of development, physiology and disease", I don't understand why the authors say: "Drop-seq protocols typically aim to incorporate about one cell in every 20 drops, so that only one drop in 400 on average receives two cells." Could someone please explain me why? I thought that 1 cell for 20 drops then, 400 drops would have 20 cells but why the author said "one drop in 400 on average receives two cells"?

Your help is really appreciated

Answer 1

[GenoMax]

While this isn't really a bioinformatics question I will answer. Drop-seq uses a nanochannel device that encapsulates the cells in liquid droplets (look for small black dots, which are cells, that get encapsulated in the droplets). Since you can't control this process precisely (as you saw from the video) you want to avoid having two cells in one droplet since that would lead to mixed data that you would need to discard. This is unavoidable at times and happens at a rate of 1 in 400 drops as indicated above.