Answer : Expression of gene means the genetic information carried by gene (in the form of DNA sequences) is utilized in the formation of functional gene product, which is usually a protein. It is accomplished through two processes that are transcription ( DNA is converted to mRNA using RNA polymerase), which is followed by translation (mRNA is converted into specific protein). The protein thus formed corresponds to particular function of the cell.
Therefore, gene expression is necessary.
A gene has two alternative forms that is dominant and recessive allele. A gene is expressed when it is present in a dominant form (that masks the expression of the recessive form).
Recessive gene is only expressed when it is present in a homozygous state (such as tt for dwarf pea plant).
Therefore, it is true saying that only some genes are expressed.
