Genomic DNA samples were fragmented using a nebulization kit (Invitrogen, K7025-05 Carlsbad, CA, USA) following the manufacturer's recommended protocol: 2.5 μg of genomic DNA was re-suspended in 750 μl Shearing Buffer (TE, pH 8.0 (Fisher Waltham MA, USA, 50843207) containing 10% glycerol (Fisher, AC15892)) and was nebulized at 6 to 10 pounds per square inch (psi) for 90 seconds to produce 2- to 4-kb DNA fragments. Fragmentation of the genomic DNA to 2 to 4 kb allows for optimal template size for performing PCR in droplets. Sheared genomic DNA was precipitated by adding 80 μl 3 M sodium acetate, pH 5.2 (Fisher, 50843081), 4 μl 20 mg/ml Mussel Glycogen (Fisher, NC9329100) and 700 μl 100% isopropanol (Fisher, AC14932). Samples were mixed by inversion and stored overnight at -20°C. The samples were centrifuged at the maximum speed (21,000 g) for 15 minutes at 4°C. The supernatant was discarded, 500 μl of cold 80% ethanol (Fisher, 5739852) wash buffer was added and the DNA pellet was spun down by centrifugation at the maximum speed for 5 minutes at 4°C. The pellet was
