1 of 27

Phylogeny�AP Topic 7.9

Learning Objectives

Describe the types of evidence that can be used to infer an evolutionary relationship
Explain how a phylogenetic tree and/or cladogram can be used to infer evolutionary relatedness

7 Natural Selection & Evolution

AP BIOLOGY

◤

2 of 27

What is phylogeny?

Phylogeny

evolutionary history of a species or group of species
shows common ancestry and how species are related over time
constructed using different types of evidence

7 Natural Selection & Evolution

AP BIOLOGY

◤

Content Knowledge

Phylogenetic trees and cladograms show evolutionary relationships among lineages

Phylogenetic trees and cladograms both show relationships between lineages, but phylogenetic trees show the amount of change over time calibrated by fossils or a molecular clock.
Traits that are either gained or lost during evolution can be used to construct phylogenetic trees and cladograms

Shared characters are present in more than one lineage.
Shared, derived characters indicate common ancestry and are informative for the construction of phylogenetic trees and cladograms.
The out-group represents the lineage that is least closely related to the remainder of the organisms in the phylogenetic tree or cladogram.

Molecular data typically provide more accurate and reliable evidence than morphological traits in the construction of phylogenetic trees or cladograms.

Phylogenetic trees and cladograms can be used to illustrate speciation that has occurred. The nodes on a tree represent the most recent common ancestor of any two groups or lineages.
Phylogenetic trees and cladograms can be constructed from morphological similarities of living or fossil species and from DNA and protein sequence similarities.
Phylogenetic trees and cladograms represent hypotheses and are constantly being revised, based on evidence

3 of 27

7 Natural Selection & Evolution

AP BIOLOGY

4 of 27

7 Natural Selection & Evolution

AP BIOLOGY

The Relationships Among Phylogeny, Classification, and Traits

5 of 27

7 Natural Selection & Evolution

AP BIOLOGY

The Relationships Among Phylogeny, Classification, and Traits

6 of 27

Evidence for Evolutionary Relationships

Morphological (Structural) Evidence
Molecular (DNA, RNA, Protein) Evidence
Developmental (Embryological) Evidence
Fossil Record

7 Natural Selection & Evolution

AP BIOLOGY

◤

7 of 27

Evidence for Evolutionary Relationships�Morphological (Structural) Evidence�

homologous structures

same structure, different function, indicating shared ancestry (e.g., forelimbs of mammals)

analogous structures

Different structure, same function, due to convergent evolution (e.g., wings of bats and insects)

vestigial structures

reduced or non-functional structures that suggest evolutionary history (e.g., whale pelvis).

7 Natural Selection & Evolution

AP BIOLOGY

◤

8 of 27

7 Natural Selection & Evolution

AP BIOLOGY

Comparing skeletal structures are homologous structures

closely related among many in related groups

Comparing the wings are analogous structures

wings of bats and birds were independently evolved characteristics

9 of 27

Evidence for Evolutionary Relationships�Molecular Evidence�

DNA, RNA, and Proteins

comparing genetic sequences (DNA or RNA) reveals evolutionary relationships
more similar the DNA, the closer the evolutionary relationship
protein similarities (e.g., cytochrome c in cellular respiration) also show relationships

Example: Humans and chimpanzees share ~98-99% DNA similarity

7 Natural Selection & Evolution

AP BIOLOGY

◤

10 of 27

DNA Sequence Alignment

7 Natural Selection & Evolution

AP BIOLOGY

◤

11 of 27

A Phylogeny Determined from Molecular Data

7 Natural Selection & Evolution

AP BIOLOGY

◤

12 of 27

Phylogenetic Trees & Cladograms�What is a Cladogram?

a simplified phylogenetic tree that shows evolutionary relationships based on shared traits

clades; groups that include a common ancestor and all its descendants

uses shared derived characteristics to organize species

7 Natural Selection & Evolution

AP BIOLOGY

◤

13 of 27

Evidence for Evolutionary Relationships�Embryological Evidence�

Zygote and Embryo Development

similar embryonic structures suggest common ancestry

e.g., all vertebrates have pharyngeal gill slits and tails at some stage

Hox genes control development and are highly conserved across species.

7 Natural Selection & Evolution

AP BIOLOGY

◤

14 of 27

Evidence for Evolutionary Relationships�Fossil Evidence�

Fossils show transitional species

connecting modern organisms to ancestors
example: Tiktaalik → Link between fish and amphibians

Radiometric dating determines fossil age, helping place species in evolutionary history

7 Natural Selection & Evolution

AP BIOLOGY

◤

15 of 27

Constructing a Cladogram: The Data

7 Natural Selection & Evolution

AP BIOLOGY

◤

16 of 27

Constructing a Cladogram

7 Natural Selection & Evolution

AP BIOLOGY

◤

17 of 27

Phylogenetic Trees & Cladograms�What is a Phylogenetic Tree?

a branching diagram that shows evolutionary history

nodes; common ancestors
branches; lineages diverging over time

can be based on morphological or molecular data

7 Natural Selection & Evolution

AP BIOLOGY

◤

18 of 27

An ancestor and its descendant populations form a lineage, shown as a line drawn on a time axis:

7 Natural Selection & Evolution

AP BIOLOGY

◤

19 of 27

When a single lineage divides into two, it is depicted as a split or node:

7 Natural Selection & Evolution

AP BIOLOGY

◤

20 of 27

As the lineages continue to split over time, the history can be represented in the form of a branching tree:

7 Natural Selection & Evolution

AP BIOLOGY

◤

21 of 27

Vertical distances between branches do not have any meaning, and the vertical order of lineages is arbitrary.

7 Natural Selection & Evolution

AP BIOLOGY

◤

22 of 27

Information in a �phylogenetic tree:

All life forms
Major evolutionary groups
Small groups of closely related species
Individuals
Populations
Genes

7 Natural Selection & Evolution

AP BIOLOGY

◤

23 of 27

Phylogenetic Trees & Cladograms�How to Read a Cladogram?

root; common ancestor
branches; show divergence of species
nodes; points where species share a common ancestor
outgroup → a species/group that is least related to the rest
organisms that share more recent nodes are more closely related

7 Natural Selection & Evolution

AP BIOLOGY

◤

24 of 27

Phylogenetic Trees & Cladograms�Interpreting Evolutionary Relationships

closer branches; closer evolutionary relationship
more shared derived traits; more recent common ancestor

Cladograms do not show time, but phylogenetic trees may

7 Natural Selection & Evolution

AP BIOLOGY

◤

25 of 27

7 Natural Selection & Evolution

AP BIOLOGY

Clades Represent All the Descendants of a Common Ancestor ��All clades are subsets of larger clades, with all of life as the most inclusive taxon. In this example, the groups called mammals, amniotes, tetrapods, and vertebrates represent successively larger clades. Only a few species within each clade are represented on this tree.

26 of 27

7 Natural Selection & Evolution

AP BIOLOGY

Inferring a Phylogenetic Tree �This phylogenetic tree was constructed from the information given in Table 16.1 using the parsimony principle. Each clade in the tree is supported by at least one shared derived trait, or synapomorphy.�

27 of 27

Summary�Phylogeny

evolutionary relationships can be inferred using morphology, DNA, embryology, and fossils
phylogenetic trees show evolutionary history based on common ancestry
cladograms use shared traits to organize organisms into clades
the closer two species are on a tree, the more closely related they are.

7 Natural Selection & Evolution

AP BIOLOGY

◤