The classification group that is made up of related species is the

Genus

Explanation:

In taxonomy, genus refers to a group of organisms that include one or more species that are closely related to each other. Organisms that are in the same genus share common features, characteristics, and/or traits but are not quite the same species. If a genus has only one species under it, it is called monotypic, but if there is more than one (which could reach more than 100 in some organisms!) it is called polytypic.

Right under genus would be species in biological organization. When naming organisms using binomial nomenclature, genus is first named, then species.  

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thinking it would be physical characteristics