Vit D is one such example of gene expression. "The actions of the vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) are mediated by the vitamin D receptor (VDR), a ligand-activated transcription factor that functions to control gene expression" [1]
So with this in mind, and knowing there are bacteria that will pretty much survive in any environment, consuming minerals which reduces availability for human consumption, how much of a humans characteristics are controlled by diet and the environment?
I would say alot. For example here in the UK, over the last 50 years, I have witnessed the reduction of dense muscle and fat in Caucasians, which in extreme will make it impossible to swim as they sink, a phenomena still seen in Black people today. [2]
Our diets are changing, and due to global food companies, food store standardisation, seed companies, agrichemical and govt legislation, people have changed quite considerably in the western world over the last 100 years, simply from the change in their diet!
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2879406 [2] https://pubmed.ncbi.nlm.nih.gov/28561485/