Chemical Biology - synthesizing/designing siRNA
At this time, it it possible to completely chemically synthesize oligonucleotides (DNA/RNA) between 30-50 base pairs. siRNAs are a class of RNAs that, as the name suggests, bind to other RNAs in a sequence specific manner. Specifically, siRNAs preferentially target mRNAs, which blocks translation of those mRNAs into proteins. This regulation of gene expression has absolutely nothing to do with "creating genes for a human being".