Which type of gene is expressed whenever it is present?

The type of gene that is expressed whenever it is present is a dominant gene. Dominant genes will manifest their traits in an organism's phenotype even when only one copy is present in the genotype. This means that if an individual has at least one dominant allele for a trait, that trait will be expressed, regardless of whether the other allele is dominant or recessive.

For example, if a dominant gene for brown eyes is present, a person will have brown eyes even if they also carry a recessive gene for blue eyes. The presence of the dominant allele overshadows the effect of the recessive allele, leading to the dominant trait being the one visibly expressed. This concept is fundamental in genetics and helps explain how certain traits are inherited from one generation to the next.

The other types of genes mentioned do not consistently result in expression. Recessive genes require two copies for their trait to be expressed, while conditional genes might only be expressed under specific environmental conditions. Anonymous genes generally refer to those whose effects or functions are not known or observable. Therefore, the correct understanding of dominant genes is crucial in genetics.