CHAPTER 26 PHYLOGENY AND SYSTEMATICS - PowerPoint Presentation

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CHAPTER 26

PHYLOGENY AND SYSTEMATICS

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What are the evolutionary relationships between a human, a mushroom, and a flower?

A phylogeny based on DNA data reveals that animals (including humans) and fungi (including mushrooms) are more closely related to each other than

to plants

.

OVERVIEW

Phylogeny is the evolutionary history of a species or group of species.The discipline of

systematics

classifies organisms and determines evolutionary relationships of living and extinct organisms.

Systematists

use fossil, molecular, and genetic data to infer evolutionary relationships3

I. Concept 26.1: Classification

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A. Taxonomy

The ordered division of organisms into categories based similarities and differences

-useful component of systematics

B. Binomial Nomenclature (two word name)

1. First proposed by

Carolus

Linnaeus

in 18

th

century

2. Two main characteristics:

a. Each species has a two-part name.

b. Species are organized hierarchically into broader and broader groups of organisms.

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3. The first part of the name is the

genus

.

4. The second part, called the specific epithet, is unique for each species within the genus.

5. Ex: Human—

Homo sapiens

which means wise man

C. Hierarchical Classification

1. Groups species into increasingly broad taxonomic categories

2. Taxonomic groups from broad to narrow are:

domain, kingdom, phylum, class, order, family, genus,

and

species

3. A taxonomic unit at any level of hierarchy is called a

taxon

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D. Phylogenetic Tree

1. Diagram used to show the evolutionary history of a group of organisms

2. Can provide important information about similar characteristics in closely related species

II. Concept 26. 2: Morphological and Molecular Data

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A. To infer relationships,

systematists

gather information about morphologies, genes, and biochemistry of living organisms

B. Organisms with similar morphologies or DNA sequences are likely to be more closely related than organisms with different structures or sequences

C. When constructing a phylogeny,

systematists

need to distinguish whether a similarity is the result of

homology

or

analogy

1. Homology

is similarity due to shared ancestry

Ex: bones of a whale’s flipper and a tiger’s paw

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2. Analogy

is similarity due to convergent evolution

Convergent evolution

occurs when two organisms developed similarities as they adapted to similar environmental challenges—not because they evolved from a common ancestor

Ex: wing of a butterfly is analogous to wing of a bat because both are adaptations for flight

3. Analogous structures or molecular sequences that evolved independently are also called

homoplasies

4. Homology can be distinguished from analogy by comparing fossil evidence and the degree of complexity

5. The more complex two similar structures are, the more likely it is that they are homologous

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D.

Molecular systematics

uses DNA and other molecular data to determine evolutionary relationships.

The more alike the DNA sequences of two organisms, the more closely related they are evolutionarily.

III. Concept 26.3: Constructing Phylogenetic Trees

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A.

Cladistics

1.

Cladistics

groups organisms by common descent

2. Once homologous characters have been identified, they can be used to infer a phylogeny

3. A

cladogram

depicts patterns of shared characteristics among

taxa

and forms the basis of a phylogenetic tree

4. A

clade

is a group of species that includes an ancestral species and all its descendants

Not all groupings of organisms qualify as clades

5. A valid clade is

monophyletic

, signifying that it consists of the ancestor species and all its descendants

MONOPHYLETIC GROUP (CLADE)

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Group I, consisting of 3 species (A, B, C) and their common ancestor (1), is a clade, also called a

monophyletic group

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A monophyletic group consists of an ancestral species and all of its descendants

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PARAPHYLETIC GROUP

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Group II is

paraphyletic.

A paraphyletic

grouping consists of an ancestral species and some, but not all, of the descendants.In this case Group II consists of an ancestral species (2) and some of its descendants (species D, E, F) but not all of them (missing species G).

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POLYPHYLETIC GROUP

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Group III is

polyphyletic.

A polyphyletic grouping consists of various species that lack a common ancestorIn this case, species D, E, F, and G share common ancestor (2), but species C has a different ancestor (1).

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B. Shared Ancestral and Shared Derived Characters

1. A

shared ancestral character

is found not only in the clade being analyzed but also in older clades

Ex: Backbone in vertebrates

2. A

shared derived character

is unique to a particular clade.

Ex: Hair in mammals

3. A character can be both ancestral and derived, depending on the context

4. When inferring evolutionary relationships, it is useful to know in which clade a shared derived character first appeared

Phylogenetic Tree

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IV. Concept 26.4: Genome Documentation(Not on exam)

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A. Comparing nucleic acids or other molecules to infer relatedness is a valuable tool for tracing organisms’ evolutionary history

B. DNA that codes for

ribosomal RNA

changes relatively

slowly

and is useful for investigating branching points hundreds of millions of years ago

C.

Mitochondrial (

mt

)DNA

evolves

rapidly

and can be used to explore recent evolutionary events

V. Concept 26.5: Molecular Clocks(not on exam)

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Molecular clocks are methods used to measure the absolute time of evolutionary change based on the observation that some genes and other regions of the genome appear to evolve at constant rates.

VI. Concept 26.6: Three-Domain System

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A. Supported by data from many sequenced genomes

B. A Comparison of the Three Domains of Life

Characteristics

Bacteria

Archaea

Eukarya

Nuclear Envelope

No

No

Yes

Membrane-enclosed organelles

No

No

Yes

Introns

No

Yes

Yes

Histone

proteins associated with DNA

No

Yes

Yes

Circular Chromosome

Yes

Yes

No

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You should now be able to:

The taxonomic categories and how they indicate relatedness

How systematics is used to develop phylogenetic trees

The three domains of life including their similarities and their differences

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