Hi @brainstorm , do you remember the problem I had generating reads during my thesis? I was generating more reads than I expected, and that was because of the meaning of this ```n``` parameter. It will generate one read pair __per chromosome__ in the genome. Which means that you'll have ```n``` reads for E.Coli, which has only one chromosome, but you'll end up with ```n*(num_chormosomes)``` reads for other organisms. I've tested for E.coli and dm3:

```
(master)guillem@Guillermos-MacBook-Air-2:~/facs/tests (master)$ cat data/synthetic_fastq/ecoli_100.fastq | wc -l
     800
```

Which is OK: 800/4 = 200 (100 paired-end reads)

```
(master)guillem@Guillermos-MacBook-Air-2:~/facs/tests (master)$ cat data/synthetic_fastq/dm3_100.fastq | wc -l
   12000
```

12000/4 = 3000 ==> 3000/2 = 1500 ==> 1500/100 = 15, num of chromosomes of Dm3.

Just take it into account :-)