Which term is used to categorize a group of similar and closely related species?

The term "genus" is used in biological classification to group species that are closely related and share a common ancestor. In the hierarchical system of classification, which includes domains, kingdoms, phyla, classes, orders, families, genera, and species, the genus is positioned above species and brings together species that exhibit similar characteristics and traits. For example, in the classification of domestic cats, the genus "Felis" includes various species such as Felis catus (the domestic cat) and Felis silvestris (the wildcat), highlighting their relatedness.

The other terms relate to genetic and biological concepts but do not define a category of related species. "Genome" refers to the complete set of genetic material in an organism, while "genotypic" refers to the genetic constitution of an organism. "Gene expression" describes the process by which the information in a gene is used to synthesize functional gene products, usually proteins. None of these terms categorize species in the way that "genus" does.