In terms of genetic traits, what is a dominant gene?

A dominant gene is defined as a gene that expresses its trait even if only one allele is present. This concept is fundamental in genetics, where alleles are different forms of a gene that can occupy the same locus on a chromosome. In the case of a dominant gene, the trait it represents will manifest in the phenotype of an organism regardless of whether the organism has one or two copies of that gene.

For example, if we consider a gene related to flower color in a plant, a dominant allele might code for red flowers. Even if the plant possesses only one allele for red flowers (and one for white), the phenotype will display red flowers because the presence of the dominant allele is sufficient for that trait to be expressed.

This understanding clarifies the nature of other gene-related options. A gene that only appears in homozygous organisms refers to a recessive gene, not a dominant one. Similarly, a gene that is not observed in the phenotype indicates that it is either recessive or not expressed at all, which does not align with the definition of dominance. Finally, a gene that requires two identical alleles to be expressed characterizes recessive traits, where the trait will only be observable when an organism is homozygous for that gene. Thus