(a) Draw a phylogenetic tree based on characters 1-5 in the...

(a) Draw a phylogenetic tree based on characters $1-5$ in the table below. Place hatch marks on the tree to indicate the origin(s) of characters $1-6 .$ (b) Assume that tuna and dolphins are sister species and redraw the phylogenetic tree accordingly. Use hatch marks to indicate the origin(s) of characters $1-6 .$ (c) How many evolutionary changes are required in each tree? Which tree is most parsimonious?

Key Concepts

Phylogenetic Trees

A phylogenetic tree is a diagram that represents evolutionary relationships among organisms based on shared characteristics. It visualizes how species diverge from common ancestors and helps in understanding evolutionary patterns, speciation events, and the order of lineage splits.

Character Mapping and Optimization

Character mapping involves assigning evolutionary changes of features or traits onto the branches of a phylogenetic tree. This process indicates where traits originate or change along the evolutionary history of the group, often using symbols or hatch marks to denote the points of change. It is fundamental for reconstructing ancestral states and discerning homologous versus convergent traits.

Parsimony Principle

The parsimony principle is a method used in phylogenetics that favors the tree requiring the fewest evolutionary changes. Under this principle, the simplest explanation, which involves the minimal number of character state transitions, is considered the most likely evolutionary scenario. It is a key criterion in evaluating and comparing alternative phylogenetic trees.

Alternative Phylogenetic Hypotheses

Considering alternative phylogenetic hypotheses involves reinterpreting relationships between taxa by altering tree topologies while still mapping characters onto the branches. Each alternative is evaluated based on the number of evolutionary changes it requires, with the goal of determining which hypothesis is most parsimonious and best fits the available data.

Transcript

00:01 Hello, we are in chapter 26 talking about phylogenetic trees.

00:06 In this video, we are going to create a couple of phylogenetic trees to compare and identify which is more parsimonious.

00:17 First, let's define what is maximum parsimony.

00:22 The principle of maximum parsimony, aka.

00:27 A .k .a.

00:27 Occam's razor is basically applied to fuzzle.

00:31 Pylogenetic trees which require the fewest evolutionary events or changes to characters between organisms now i've created a tree using these characters on the left and these organisms on the right we're going to place the characters using hatchmarks to indicate evolutionary events so we have the lanclet, our outgroup, which is a type of invertebrate, comparing to our lamprey, which is a vertebrate.

01:17 So we would place number one backbone, character backbone, right here, because that's where they have diverged.

01:27 We're going to place number two, hinge jaw here between the lamprey and the tuna's ancestor.

01:36 And we're just going to go down the line here.

01:40 We have number three for four limbs between the tuna and the salamander.

01:45 Number four, the amnion, which is like the amniotic sack, which we're familiar with, with babies and eggs.

01:55 It just protects the embryo.

01:58 Number five, milk, when mammals started producing milk.

02:03 I'm going to put that before the leopard and the dolphin.

02:06 Now number six, the dorsal fin is going to go here and up by the tuna because they both have dorsal fins...

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