Final answer:
The term for genes related by a common ancestral gene is 'homologous'. Homologous traits demonstrate a shared evolutionary history, in contrast to analogous traits which arise independently. Shared derived traits are key in cladistics for determining evolutionary relationships.
Step-by-step explanation:
The term that describes genes (and gene products) related by a common ancestral gene is B. Homologous. Homologous traits, including both genes and structural features, indicate that species share a common ancestry and an evolutionary path. This contrasts with analogous traits, which arise when different species develop similar characteristics independently, usually as a response to similar environmental pressures and not due to a close evolutionary relationship. Vestigial structures, such as the hind leg bones in whales mentioned in the provided information, also support the idea of common ancestry, offering evidence for the evolution of species from a common point.
When considering cladistics, which is the classification of species based on evolutionary relationships, the important traits to consider are a. shared derived traits. These traits are unique to particular groups of organisms and provide insight into their evolutionary paths, distinguishing them from shared ancestral traits, which are older and more general features found in a wider range of related species.