Which term describes genes that guide the expression of structural genes without coding for a protein themselves?

• A. Regulatory genes
• B. Structural genes
• C. Genotype
• D. Phenotype

Answer: (A)

Regulatory genes control when and how much structural genes are expressed by producing regulators that interact with DNA to increase or decrease transcription. They don’t become the structural proteins themselves; instead, their products guide the activity of structural genes, ensuring the right genes are turned on or off in the right cells and contexts. For example, transcription factors produced by regulatory genes can bind to promoters or operators to modulate transcription of the enzymes or other structural proteins those genes encode. The other terms describe different ideas: structural genes are the ones that code for proteins themselves; genotype refers to the genetic makeup, and phenotype to the observable traits.