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Paraphyletic Group: Definition & Overview

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  • 1:11 How to Read a Phylogeny
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Lesson Transcript
Instructor: Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

A paraphyletic group is a group of organisms that includes an ancestor but not all of its descendants. Learn more about paraphyletic groups and some examples of them in this lesson.

Definition

Phylogenetics is a branch of biology that deals with studying and determining the evolutionary relationships, or patterns of descent, of groups of organisms. There are three types of phylogenetic groups:

  1. Monophyletic group: contains an ancestor and all of its descendants
  2. Paraphyletic group: contains an ancestor but only some of its descendants
  3. Polyphyletic group: contains various organisms with no recent common ancestor

We will focus mainly on paraphyletic groups for the rest of this lesson. A paraphyletic group is kind of like a group that consists of your parents and your siblings but not you. Your parents are the ancestors of the group, and the descendants are you and your siblings. If you or any one of your brothers or sisters were left out of the group, it would be paraphyletic because it includes ancestors and only some of the descendants. In phylogenetics, however, the term paraphyletic (or monophyletic or polyphyletic) is usually used when describing a group of species and their evolutionary ancestors and not just a small family unit.

How to Read a Phylogeny

The three kinds of phylogenetic groups can be better understood by using a diagram called a phylogenetic tree. A phylogenetic tree, or simply phylogeny, is a branching diagram that shows the evolutionary relationships of ancestors and their descendants. The recent common ancestor of all the descendants in the tree is represented by the root. Descendant organisms are labeled at the tips of the phylogeny. A node indicates a divergence event and splits into two branches. A node also represents a common ancestor for the descendants that branch off of it.

Using A Phylogeny to Illustrate a Paraphyletic Group

The phylogeny diagram depicts each of the three types of phylogenetic groups. Descendants D and E (in purple) represent a monophyletic group. Descendants B and C, together in orange, represent a polyphyletic group. The yellow group that includes descendants B, C, D, and E is a paraphyletic group.

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