Question

If a phylogenetic tree depicts extant taxa on the right and the point of most recent common ancestry on the left, what does the vertical axis represent?

1) Time
2) Taxa
3) Most recent common ancestor
4) Cannot be determined

Answer 1

The vertical axis of a phylogenetic tree does not typically represent anything consistently, such as time or taxa, and cannot be determined unless specified. (option 4)

Step-by-step explanation:

If a phylogenetic tree depicts extant taxa on the right and the point of most recent common ancestry on the left, the vertical axis typically does not have a consistent meaning; it is simply there to separate the lineages visually. However, it could potentially represent time if the phylogenetic tree is specifically drawn to scale in terms of time. Otherwise, without additional information specifying that the vertical axis represents time, the answer would be 4) Cannot be determined.

It is crucial to understand that phylogenetic trees can be either 'rooted' or 'unrooted'. A rooted phylogenetic tree has a single ancestral lineage from which all organisms represented in the diagram relate. This ancestral lineage is typically drawn from the bottom or left. In contrast, 'unrooted' trees do not show a common ancestor but do show relationships among species.

The branches of a phylogenetic tree represent the evolutionary relationships and order in which divergences took place, and not necessarily the lengths of time between those events unless otherwise indicated. As such, a phylogenetic tree explains the evolutionary history and can demonstrate how closely related certain species are based on their characteristics.