Question

Every node in a phylogenetic tree represents a(n) ________.

1) sister species

2) common ancestor

3) extinction event

4) transitional form

Answer 1

Every node in a phylogenetic tree represents a common ancestor. The tree depicts evolutionary relationships based on nodes where an ancestral species diverged into two new species. Species relatedness is inferred by how close their branch points are to each other.

Step-by-step explanation:

Every node in a phylogenetic tree represents a common ancestor. A phylogenetic tree is a diagram that shows how species are related to each other through common ancestors. The internal nodes of this tree denote points in evolution when it is believed an ancestor diverged to form two new species. When looking at a phylogenetic tree to determine the relationship between species, one can infer that Species 1 and 2 are more closely related to each other than either is to Species 3 by observing that Species 1 and 2 stem from the same branch point after the divergence with the branch leading to Species 3.

The length of each branch in the phylogenetic tree is proportional to the time that has passed since that specific divergence occurred. This relates to the passing of time and represents the evolutionary history of the species. Moreover, the root of a phylogenetic tree indicates an ancestral lineage that gave rise to all organisms on the tree, and branch points denote where lineages diverged.