To reduce the amount of erroneous bases, both paired-end datasets were
processed by (i) removing Ns from both ends, (ii) clipping bases with
a Sanger quality ≤10 and (iii) removing reads with more than six bases
with Sanger quality ≤10 after steps (i) and (ii), leading to a total
of 30 940 088 and 64 441 708 reads for human and mouse, respectively.
I'm a bit confused as to what (ii) means. Any insight?
Now, your read has bad quality = 2 (<=10) in the beginning and in the end. This means these bases are not reliable. So, those bases will be clipped resulting in the clipped sequence:
Clipping bases in this case just means trimming/masking. So removing base calls with quality below a threshold. Typically this is occurring at the 5' and 3' ends of reads so you trim inwards to remove the low quality calls
Thanks for the answer and example!