Define a clade and explain what a synapomorphy is in phylogenetics.

Define a clade and explain what a synapomorphy is in phylogenetics.

• A. A clade is a monophyletic group consisting of an ancestor and all its descendants; a synapomorphy is a shared derived trait that defines a clade
• B. A clade is any non-monophyletic grouping; a synapomorphy is a trait that defines a group with multiple origins
• C. A clade is a random collection of species; a synapomorphy is a primitive trait shared by all members
• D. A clade is a lineage with no descendants; a synapomorphy is a trait that evolved late

Answer: (A)

Clades are monophyletic groups, meaning they include a common ancestor and all of its descendants. A synapomorphy is a shared derived trait that originated in that most recent common ancestor and is inherited by all its descendants, so it serves as a diagnostic feature that defines the clade on a phylogenetic tree. This combination—a monophyletic grouping plus a shared derived character that unites its members—lets us infer evolutionary relationships and distinguish one clade from others. For example, mammals are grouped together in part because they share derived traits like mammary glands and hair that arose in their common ancestor. Traits that aren’t derived within the group (ancestral traits) or that arise independently in different lineages (convergent traits) don’t define a clade, which is why the described definition is the best fit.

Clades are monophyletic groups, meaning they include a common ancestor and all of its descendants. A synapomorphy is a shared derived trait that originated in that most recent common ancestor and is inherited by all its descendants, so it serves as a diagnostic feature that defines the clade on a phylogenetic tree. This combination—a monophyletic grouping plus a shared derived character that unites its members—lets us infer evolutionary relationships and distinguish one clade from others. For example, mammals are grouped together in part because they share derived traits like mammary glands and hair that arose in their common ancestor. Traits that aren’t derived within the group (ancestral traits) or that arise independently in different lineages (convergent traits) don’t define a clade, which is why the described definition is the best fit.