Lab 3: Shared Characters and Phylogeny

Students will identify shared morphological characters and use these to create a phylogenetic tree.

Module Objectives (MO3.1, MO3.3, MO3.4):

1. Differentiate between, explain the significance of, and give examples of, homologous and analogous traits.
2. Explain how shared characteristics (homologous traits) and DNA are used to construct phylogenies.
3. Apply the basic rules of Phylogenetic Systematics (cladistics) to show evolutionary relationships among taxa.

Lab Objectives:

1. Recognize and list homologous traits shared between taxa.
2. Recognize and list analogous traits shared between taxa.
3. Create a phylogenetic tree to illustrate hypothetical evolutionary relationships among taxa

Part 2: Creating a tree

Using Table 2 from Part 1 (provided below), you will create a phylogenetic tree. This tree can be neatly hand-drawn (you can take a picture of it and paste it into this report at the end).

Table 2

	B	C	D	E	F	G	H	I
A	2	0	1	2	2	1	2	2
B		2	3	2	2	3	0	2
C			1	2	2	1	1	2
D				2	2	0	3	2
E					0	2	2	1
F						2	2	1
G							3	2
H								2

1. Begin by identifying the most closely related taxa. These will be the pair or pairs of organisms that have the least number of differences between them. Place these pairs at the top of the tree.

Example, consider that taxa X and Y have only one difference between them. They will be placed next to each other at the top of the tree. They shared a common ancestor relatively recently, so that should be shown as a dot below them that then leads separately to X and Y. Likewise, taxa S and V also have just one difference between them. They would also be considered very closely related, and they would share a recent common ancestor (though this ancestor would be different from the one shared by X and Y).

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