Yes, gene expression can be altered. Gene expression refers to the reading of genes to assemble and create relevant protein products that the cell needs. 

Genes can be altered by a variety of environmental factors including temperature, light, food, drugs, chemicals, and exposure to toxins. The gene alterations can range from minor and temporary to major and permanent. Some changes are significant enough to cause genes in the system to be wrongly turned off or on, resulting in adverse reactions.  

Alterations in gene expression can be passed on from parent to child.