Final answer:
The correct option is c. A group consisting of a common ancestor and all of its descendants is termed a clade, which is a key concept in phylogenetics, representing monophyletic groups in a phylogenetic tree.
Step-by-step explanation:
A group consisting of a common ancestor and all of its descendants is known as a clade. This term refers to a group of organisms that represents a single ancestor and all its descendants, thus forming a monophyletic group. The concept of clades is a fundamental aspect of phylogenetics, which is the study of the evolutionary history and relationship between different species or groups of species.
To further clarify, a clade is not only about genetic similarities but also about an evolutionary lineage that can be represented on a phylogenetic tree, where each branch point (or node) represents a divergence from a common ancestor. It is a way of showing evolutionary relationships through common descent based on the analysis of shared derived traits. Therefore, clades can contain multiple groups or a single group, but importantly, all organisms within a clade stem from a single point on a phylogenetic tree.