There’s an additional, less-studied level of contol that may be at play too: epigenetics. Epigenetics looks at the expression (frequency of use) of genes as they are transcribed to make proteins. That is, other specific proteins may attach to the DNA, turning up and down the frequency at which it is transcribed into RNA to then make the proteins such as the serotonin transporter discussed in your article. I’m not aware of any research yet into the epigenetics of genes related to depression, but there’s an interesting article on epigenetics in general in the current Scientic American MIND.

Thanks for covering these topics.

You use the terms “allele” and “gene” interchangeably, which is also incorrect, as an allele is a common variation in a gene, not a gene itself. When talking of SLC6A4 the term gene is the correct one. When talking about the part of the gene that varies, you want the acronym 5-HTTLPR (serotonin transporter gene promoter region).